Democratic Congresswoman Eddie Bernice Johnson, who represents Dallas, has called on Congress to take action against gun violence following the shootings.

Police are sweeping parts of downtown Dallas for explosives after a suspect told officers he had planted devices in the area.

Major Max Geron, a senior Dallas police officer, said the search would take "quite a while".

Dallas sports reporter Mike Leslie has tweeted this photo of officers lining up to salute police casualties at a hospital.

This is the deadliest day for US police in the US since 9/11, according to records published by the National Law Enforcement Officers Memorial Fund, external.

Seventy-two police officers died on that day - 71 at the World Trade Center and one aboard United Airlines flight 93. 

Five police officers have died in the attack in Dallas and six are in hospital.

Media and prominent figures in Dallas have been using the hashtag #DallasStrong on Twitter to express their solidarity with police and fellow citizens.

The three Dart (Dallas Area Rapid Transit) officers injured in the shooting have been named as Omar Cannon, 44; Misty McBride, 32; and Jesus Retana, 39. 

All three are expected to survive, according to the Dallas Morning News.

One Dart officer was among the five killed. He was named earlier as Brent Thompson, 43.

Amateur video footage has emerged which appears to show one of the gunmen shooting outside the El Centro college building.

Image source, Google

The suspect who was involved in a stand-off with police in a Dallas parking garage is now dead, according to multiple local media reports.

Police have not confirmed the reports.

The suspect was one of four believed to have launched a co-ordinated attack to kill Dallas police officers. The other three suspects are all in custody.

An eyewitness has described running from the "rapid fire" as the gunmen started shooting.

Speaking to Dallas news channel WFAA-TV, the unnamed man said:

"We heard gunfire and at first you didn't really realise what you were hearing. You know, you thought it was something like something popping and then you heard rapid fire and then everybody realised it and just took off running. 

"Everybody just ran their own separate ways and what we tried to do was try to get the women and the children back there in the protest away from the gunfire. They were running toward it. 

"We had to get them back in the traffic. We had to back the traffic back. It was a horrifying experience to see all those people running and not knowing where the bullets were coming from."

The shootings occurred around Main Street, where a protest was taking place following the earlier killing of two black men by police in Louisiana and Minnesota.

The suspects fired at police officers from elevated positions in a parking garage overlooking the street. 

Nearby El Centro College was placed on lockdown ahead of the protest and remained in that state for several hours.

Three suspects are in police custody and one remains in a stand-off with police in the parking garage. Some reports say that fourth suspect has now died but this has not been confirmed. 

Shetamia Taylor, a mother of four, was shot in the leg during the attack. Speaking to a local TV station, her sister described the moment Shetamia was hit and dived on one of her sons to cover him:

"As the rally was ending and they turned to leave, they were one of the first crowds to leave, they heard the first gunshot. After that first gunshot she heard the second gunshot and after that it was just a lot of gunshots. She said they just came so fast and they wouldn't stop. 

"They all began to run, scatter and she said as she started to run she caught a bullet in the back of her right leg. She immediately jumped on top of one of her boys, the 15-year-old, she jumped on top to cover him on the ground as she pushed him in between two cars and the kerb.

"Her other three boys scattered and ran in opposite directions. So she lost three of her boys, didn't know where they were. She lay there, she said it was about five minutes before cops even got to her and pulled her from the area where she was because the shots were coming so fast." 

Here's video of the earlier press conference with Dallas police chief David Brown.

President Barack Obama, who is in Poland for the Nato summit, is being briefed on the situation in Dallas, the White House has said. 

White House spokesman Josh Earnest said: "The president has been updated on the shooting of police officers in Dallas. He asked his team to keep him updated on the situation as they get additional information." 

Dallas Morning News has published a picture of Brent Thompson, the first victim named by police.

Thompson, 43, was an officer with the Dallas Area Rapid Transit force.

The other four officers killed in the attack have not been named.

The Dallas Police Department has now confirmed the death of a fifth officer.

Dart - the Dallas Area Rapid Transit - has confirmed the name of the officer it lost in the attack as Brent Thompson, 43.

He is the first Dart officer to die in the line of duty.

Of the five officers known to have died, four were from the Dallas Police Department and one from Dart.

Several reports from Dallas journalists suggest a police operation is under way to end the standoff with the final suspect, although there is no confirmation yet from police.

Dallas Police say a fifth officer has died. 

Six officers remain in hospital.

A man who turned himself in after Dallas police released an image of him in relation to the shooting has now been released by police.

Mark Hughes, the brother of protest organiser Cory Hughes, attended the protest openly carrying a rifle.

Interviewed on local television, Mr Hughes said he spoke to police shortly after his brother's image was released and his brother later turned himself in.