The man arrested by Humberside police is the captain of the Solong cargo ship, the vessel's owner tells the BBC
Earlier, the police force said that a 59-year-old man has been arrested on suspicion of gross negligence manslaughter, following the North Sea collision
Assistant Chief Coastguard John Craig says flames are still visible on the Solong, with salvage plans in place for both vessels
One crew member of the Portuguese cargo ship is "assumed deceased", a UK minister says, as the transport secretary says both Solong and US oil tanker Stena Immaculate are expected to stay afloat
Owners of the cargo ship say it was not carrying sodium cyanide, as previously reported, but had four empty containers that had once held the toxic chemical
Watch: Charred container ship and oil tanker seen from above
Alastair Smith, head of operations for Lincolnshire at East Midlands Ambulance Service, says emergency crews assessed 36 people at Grimsby's North Quay earlier after receiving a call at 11:28 GMT.
He adds that nobody was required to go to hospital.
Earlier, MP Graham Stuart said one person had been hospitalised.
Rachel Flynn
Live reporter
Esme Stallard
Climate and science reporter
As we've reported, the Solong cargo ship was carrying 15 containers of the chemical sodium cyanide when it collided with the Stena Immaculate tanker.
Sodium cyanide has a variety of commercial uses, from being used to plate metals to dye production.
Dr Mark Hartl, associate professor of marine biology at Herriot Watt University, explains that sodium cyanide is very soluble in water and can be toxic because it interferes with the respiration of animals.
At this point it is not clear if any has entered the water or been burnt, but it has the potential to kill aquatic organisms through ingestion.
Dr Hartl did explain that marine organisms like fish have a major avoidance reaction so may have already vacated the area.
This morning, the Humber Coastguard appeared to make a distress call via radio to alert other ships in the area that "Solong has collided with tanker Stena Immaculate".
The Coastguard asked for vessels with firefighting equipment or search and rescue capabilities to assist, at the time when crews were evacuating. You can listen to that recording here:
The Solong vessel was carrying 15 containers of the chemical sodium cyanide among other cargo, when it collided with the Stena Immaculate tanker in the North Sea earlier, according to a report from maritime data provider Lloyd’s List Intelligence.
The UK Health Security Agency (UKHSA), describes sodium cyanide as a white crystal-like solid with a faint almond odour. It is used in industry for metal cleaning, plating and extraction, and photography. It can also be used to make other chemicals.
The agency says exposure to cyanide salts can cause headache, nausea, dizziness, nervousness, confusion, changes in heart rate and drowsiness. In the most serious cases, there can be heart and breathing problems or even death, it adds.
As we've been reporting, the two ships involved in the collision are the oil tanker MV Stena Immaculate and a cargo ship called Solong. Here is a graphic to help you understand how they compare:
One of the ships involved in today's collision, the MV Stena Immaculate oil tanker, was carrying cargo for the US Department of Defense, US officials have confirmed.
"The collision and ensuing explosions will not impact operations or combat readiness. We do not have a single point of failure," the officials say.
We've also heard from the ship company's owner that the vessel was carrying jet fuel when it was hit by the Solong.
Rowan Bridge
Reporting from Grimsby
Image source, ReutersIt's very much a closed off scene here at the moment.
The dock behind me has now been shut and no commercial vessels are going in or out of it.
In the last hour, we've had a statement from the owners of the Stena Immaculate saying there were multiple explosions on the tanker and it is now pouring jet fuel into the North Sea.
The coastguard say they are assessing what pollution response might be needed.
There will be questions about what conditions were like out at sea this morning, but this happened during daylight.
The Stena Immaculate was anchored off the coast of Hull, when it and the cargo ship Solong collided.
We are yet to hear any response from its owners about what has happened here today.
Downing Street says details of the cause of the collision are "still becoming clear", with a spokesperson for the prime minister describing the crash as an "extremely concerning situation".
The spokesperson adds: "We thank the emergency services for their rapid response. I understand the Department for Transport is working closely with the coastguard to help support the response to the incident.
"We're obviously monitoring the situation, we'll continue to co-ordinate the response and we're grateful to emergency personnel for their continued efforts."
The Marine Accident Investigation Branch has deployed a team to conduct a preliminary assessment, as we reported earlier.
Baroness Susan Hayman, Parliamentary Under-Secretary of State at the Department for Environment, says she is "extremely shocked and concerned" about the North Sea collision.
Speaking in Parliament, Hayman calls the situation an "emerging picture" and says the department is speaking closely with the Department for Environment, Food & Rural Affairs (Defra) and the Department for Transport and Maritime and Coastguard Agency.
Hayman also says the Environment Agency is engaging with any clean-up needed.
Independent maritime safety consultant David Mcfarlane tells BBC News that more will become clear once investigators can get on board the vessels and recover data recorders.
But, he says, "there should be no reason for two ships to collide".
There are collision regulations in place to avoid situations like this - and Mcfarlane says "something has gone very badly wrong".
These vessels are "quite manoeuvrable", and the speed the Solong was travelling at was about average speed.
He says it is common for ships to be on autopilot, but there should always be someone on watch.
It will take "weeks if not months to come to any proper conclusion".
On the spill of jet fuel, Mcfarlane says it is "fairly light" compared to the likes of crude oil. This means there will be less pollution than if it were another type, but there will "still be another oil spill, there's no doubt about that", he adds.
Image source, RSPBDave O’Hara, senior site manager at the Royal Society for the Protection of Birds (RSPB) Bempton Cliffs, says the incident has taken place in an area home to England's largest gannet colony and internationally important populations of seabirds.
"Naturally, we are extremely concerned about the potential for a leak from the tanker as oil pollution can seriously damage habitats and be lethal to seabirds," he says.
They are keeping a close eye on the situation.
Around half a million seabirds, including Gannets, Kittiwakes, Guillemots, Razorbills and Puffins breed in the area each year, on the 400-foot-high (122 metre) chalk cliffs.
The Cleethorpes Wildlife Rescue committee is preparing in case they are needed to rescue wildlife affected by the fuel spill caused by the collision this morning.
In a post online, it says they have met to discuss how best to help wildlife, particularly birds, that may reach Cleethorpes Beach.
The group says it is adapting its oil spill response protocols to be prepared for this incident and has set up "a dedicated oiled wildlife hotline for reporting affected animals in Cleethorpes: 01472 472662".
They have also scheduled a meeting with partner rescue group and will be closed for the rest of Monday to work on preparation.
"If you spot an oiled bird along our coast, please do not attempt to handle it. Instead, report the sighting via the hotline, and a volunteer will respond as soon as possible", the committee says.
Greenpeace UK says it is "too early" to know the extent of any environmental damage caused by the incident, but "both the high speed of the collision and the footage of the aftermath are cause for great concern".
A spokesperson says any impact relies on a number of factors, including what type of oil was released and how much of it is in the water.
"Sea and weather conditions will also be important in determining how any spill behaves", the spokesperson says.
"In the case of an oil spill or any loss of hazardous cargo from the container ship involved, the speed of the response will also be crucial in limiting any impact."
Niall Stevenson saw crews arriving at the scene
We've just heard that only one crew member is in hospital following the incident earlier.
Local worker Niall Stevenson tells the BBC he saw a "load of ambulances" and search and rescue crews pulling up shortly after 09:30 GMT this morning.
He says there were about eight or nine ambulances, and some police on the scene too.
"It was a full hands on deck" situation, he adds.
Local MP Graham Stuart says he has spoken to the transport secretary and only one person has been hospitalised.
"The other 36 mariners across both crews are safe and accounted for," he adds.
Everyone is now on shore, but Stuart says he is concerned about the "potential ecological impact".
He says he is "calling for a unified command structure, to bring together government, police, Coast Guard, the Environment Agency, local authorities and your MPs".
As we've been reporting, an oil tanker involved in the collision with a cargo vessel off East Yorkshire's coast is on fire.
The two ships involved are the oil tanker MV Stena Immaculate and a cargo ship called Solong. The Immaculate was carrying jet fuel - the company that owns the ship says this is now leaking into the sea.
All of the crew from the Immaculate have been rescued safely - there were more than 20 people on board.
So far, 32 people have been brought to shore. They are being taken away in ambulances and their condition is unknown.
A coastguard rescue helicopter from Humberside has been on scene alongside a Coastguard fixed-wing aircraft and nearby vessels with firefighting capability and lifeboats have been dispatched from Skegness, Bridlington, Mablethorpe and Cleethorpes.
The alarm was first raised at 09:48 this morning, and marine inspectors are already gathering evidence to determine the next steps.
We'll continue to bring you the latest as soon as we have it.
Jonathan Josephs
Business reporter
US logistics firm Crowley, which is the operator and joint owner of the MV Stena Immaculate, says the vessel was carrying jet fuel when it was hit by the Solong in the North Sea at approximately 10:00 GMT.
All of its crew of more than 20 are now safe and accounted for - but there are fears that jet fuel is now pouring into the sea.
In a statement, the Florida-based company said: “A fire occurred as a result of the allision, and fuel was reported released. The Stena Immaculate crew abandoned the vessel following multiple explosions onboard. All Crowley mariners are safe and fully accounted for.”
I understand this jet fuel was owned by the US government. That’s consistent with the vessel being part of a US government programme designed to supply the armed forces with fuel during times of armed conflict or national emergency.
The US Air Force has several bases in the UK.
We're starting to get some more images from the scene of the collision now.
They show a large fire that is spread across the North Sea and thick black smoke billowing upwards. A rescue vessel appears to be spraying the blaze with water.
Image source, PA Media
Image source, PA MediaEvidence is being gathered and next steps are being determined following the collision of the two vessels in the North Sea, marine inspectors say.
A spokesperson for the Marine Accident Investigation Branch says it has deployed a team to Grimsby following this morning's collision of the container ship Solong and the oil tanker Stena Immaculate.
"Our team of inspectors and support staff are gathering evidence and undertaking a preliminary assessment of the accident to determine our next steps," it adds.