This is only the fourth time in US history that an impeachment inquiry has been launched against a president.

The inquiry is investigating whether Trump abused his presidential power by pressuring the president of Ukraine to investigate his potential 2020 rival Joe Biden.

Two House Democrats - Collin Peterson of Minnesota and Jeff Van Drew of New Jersey - defected from their party and voted against the resolution.

Justin Amash, a former Republican who became an independent earlier this year, voted in favour of the impeachment resolution.

"What is at stake in all of this is nothing less than our democracy," Pelosi said on the floor of the House of Representatives.

"I don’t know why the Republicans are afraid of the truth."

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At an earlier press conference she said: "It's a sad day - no-one comes to Congress to impeach a president."

House Republican Leader Kevin McCarthy said: "This impeachment is not only an attempt to undo the last election, it's an attempt to influence the next one as well."

The White House immediately blasted the vote, saying Democrats were wasting time on a "sham impeachment - a blatantly partisan attempt to destroy the president".

"With today’s vote, Speaker Pelosi and the Democrats have done nothing more than enshrine unacceptable violations of due process into House rules," White House press secretary Stephanie Grisham said.

"The Democrats want to render a verdict without giving the administration a chance to mount a defense. That is unfair, unconstitutional, and fundamentally un-American."

Pelosi announced an impeachment inquiry into Trump in September, but this was esentially a rebranding of existing committee investigations.

Republicans had attacked Democrats for not officially authorising the inquiry with a House vote, as happened with presidents Richard Nixon and Bill Clinton.

They have also blasted the Democrats for holding hearings behind closed doors.

The resolution passed on Thursday allows the impeachment process to a more public stage.

It authorises the House Intelligence Committee - the panel that has been leading the impeachment investigation - to convene televised hearings and release transcripts of the private depositions that have taken place so far.

The Intelligence Committee will then send a report to the House Judiciary Committee, which would draft articles of impeachment.

Impeachment operates similarly to a criminal indictment.

If the House voted to impeach Trump, the process would then head to a Senate trial. It would require a two-thirds vote in the Republican-controlled Senate to remove Trump from office.