"I created records after conversations, and I think I did it for all of our nine conversations," says Comey.

"I knew the there would come a day that I might need a record, not just to defend myself, but to defend the FBI."

About his Oval Office meeting with Trump when president told Attorney General to leave, Comey says: "Something big is about to happen. I need to remember every single word that is spoken."

He spoke with Obama twice, but never documented the meetings, he says.

He also never felt the need to document meetings with President George W Bush.

Mark Warner, Democratic committee vice-chairman, asks what was it about Comey's meeting with Trump that led him to take notes?

Comey says it was "a combination of things, the circumstances, the subject matter, and the person I was with".

The circumstances: I was alone with the president-elect of the United States.

The subject matter: "It was matters that touch on the core responsibility of the FBI and related directly to the president-elect."

Then something of a bombshell:

The person I was with: "I was honestly concerned that he might lie about the nature of our meeting."

He says the three things led him to want to take immediate notes, something he had never felt the need to do with any previous president.

Comey says he is "sure" Robert Mueller, the special counsel leading an independent investigation into ties between Trump campaign and Russian officials, is examining whether Trump obstructed justice.

The former FBI director says he has no doubt Mueller is one of the country's "great, great pros".

Comey says he has full confidence in the special counsel investigation.

The appointment of Robert Mueller, who led the FBI for more than a decade, came just over a week after Trump fired Comey - sparking calls for such a move.

Senator Burr returns to Comey’s decision to talk publicly about Clinton emails.

Mr Comey says he was "confused and concerned" that then-Attorney General Loretta Lynch directed Comey to call the Clinton email affair not an investigation but a "matter".

That "confused and concerned me", Comey says, and was "one of the bricks in the load" that convinced him to bypass the Justice Department.

Question: How many entities were targeted by Russian hackers?

Comey says "at least hundreds" of US institutions were targeted by a massive Russian spearfishing campaign during campaign, "possibly thousands".

Comey says he first became aware of Russian cyber-intrusion in summer 2015, and says it was later that year that he heard of data theft.

Question: "If you look back, would you change the way you handled the Clinton email affair?"

Comey: "Honestly no. It caused a lot of personal pain but when I look back I think it was the best way to protect the justice institution including the FBI."

Plenty of social media users are comparing this spectacle to the US TV series House of Cards.

And, of course, the House of Cards Twitter account never misses a trick ...

Comey says he won't go into the salacious allegations put forward by a former British intelligence official because of the details.

In January, Buzzfeed published a dossier compiled by the investigator, Christopher Steele, alleging that Moscow had compromising material on the then-president-elect, making him liable to blackmail.

Among the various memos in the dossier was an allegation that Mr Trump had been recorded by Russian security services consorting with prostitutes at a Moscow hotel.

• Comey says he is confident no votes cast in the 2016 election were altered
• But he has no doubt Russia meddled in the US election
• He does not think Trump actually asked him to drop the Russia investigation
• Adds it is not for him to say whether the president tried to obstruct justice

Comey finished by paying tribute to his FBI colleagues.

"The FBI is honest, the FBI is strong, and the FBI is and always will be independent," says Comey who also thanks his colleagues for their service.

He also apologises for not having had the opportunity to say goodbye more formally.

Comey says he will not repeat his prepared remarks.

A conciliatory beginning: Comey says he understands that the president holds the right to fire an FBI director at any time in their 10-year term

But he says the explanations for his sacking "confused and increasingly concerned" him.

The president repeatedly told him he was doing a great job, and told others he was doing a great job.

"So it confused me when I saw on television that the president fired me because of the Russia investigation.... That didn't make sense to me."

He says the president defamed him and the FBI, saying the agency wasn't doing its job.

"Those were lies plain and simple."

This is already searing stuff.

Trump expressed "an odd and unexplained affection for the Russian dictator," says Warner, referring to Vladimir Putin.

Warner calls Comey's description of his interactions with the president "very disturbing".

"The president appeared to be making an effort to influence or at least co-opt the leader of the FBI," Warner says.

"Think about it, the President of the United States, asking the FBI director to drop an ongoing investigation."

On Trump's alleged request to Comey to drop the Mike Flynn probe, Warner says: "Think about it, the president of the United States asking the director of the FBI to drop an ongoing investigation."

Warner says Trump's explanation for firing Comey - that he didn't agree with his handling of Hillary Clinton's email investigation - "didn’t pass any smell test".

He also reminded Comey about the time that Trump reportedly called him "a nut job".

Comey's face remains blank as Warner goes on.

Image source, AFP / Getty Images

Senator Mark Warner, Virginia, Democratic vice-chairman of the committee, says: "This investigation is not about re-litigating the election.

"It's not about who won or lost, and it's sure as heck not about Democrats versus Republicans.

"We're here because a foreign adversary attacked us right here at home", he says, adding that it was not done with guns or missiles.

Sen Warner praises Comey, saying that the way he was fired by the president was "ultimately shocking".

He rounds on Trump and his associates (Michael Flynn, Jeff Sessions, and Jared Kushner) for their interactions with Russians.

Sen Richard Burr has some questions for Comey.

Did the president’s request for loyalty or to lift the cloud of the Russia investigation alter your approach to the Russia investigation?

Did you find any evidence of collusion between the Trump campaign and Russia?

Why did you decide to publicly announce that the Dept of Justice had decided not to pursue charges on Clinton emails?

Image source, AFP / Getty Images

Sen Richard Burr, the Republican committee chairman, introduces the hearings. He tells Comey this is his opportunity to set the record straight about his meetings with the president.

"Americans need to hear your side of the story, just as they need to hear the president's description of events," says Burr.

"We will establish the facts separate from rampant speculation, and lay them out for the American people to make their own judgement."

Image source, AFP/Getty Images

Image source, Pool

The former FBI director is sitting stony faced for the cameras. He's scheduled for three hours of testimony.

Image source, Zvezda TV

"Trump’s only questionable request was that Michael Flynn be left alone after losing his job,” said the Russian Defence Ministry’s Zvezda TV.

"Donald Trump never interfered in an investigation of his ties with Russia... More than that, Comey said Trump had personally insisted that the public be regularly informed of the progress of the investigation," Zvezda added.

According to official Rossiya 24 TV, the main thrust of Comey’s statement is that Trump himself is not under investigation over his alleged links to Russia.

"The question that has preoccupied the Americans' minds for so long has finally been answered thanks to testimony by [former] FBI chief James Comey," Rossiya 24 TV said.

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Preet Bharara, the former US Attorney for the Southern District of New York, who was fired by Trump, has managed to bag a seat.

On #ComeyDay, let's take a look at what President Trump's up to.

Starting at 11:30, Trump will be visiting the religious conservative Faith & Freedom Coalition’s Road to Majority conference in Washington DC ,where he is due to make remarks.

At 15:30 he will be holding an "infrastructure summit" with mayors and state governors.

Quite a few people are hoping that Trump will take to his favourite medium, Twitter, to comment on the hearing.