Bernie Sanders has confirmed he's entering the 2020 US presidential race.

The independent senator will seek the Democratic nomination for a second time.

He was the surprise runner-up in 2016, but despite significant grassroots support for the Vermont senator the nomination ultimately went to Hillary Clinton.

Announcing his bid, he told Vermont Public Radio: "I think the current occupant of the White House is an embarrassment to our country.

"I think he is a pathological liar every day... It gives me no pleasure to say that.

"But I also think he is a racist, a sexist, a homophobe, a xenophobe... somebody who is gaining cheap political points by trying to pick on minorities, often undocumented immigrants."

He added the second main reason he's running is that many of the ideas he highlighted in 2016 - such as Medicare for All and tackling climate change - have only become more popular in the US.

He said: "We began the political revolution in the 2016 campaign... now it's time to move that revolution forward."

'Transforming our country'

In his campaign launch video, he added: "Our campaign is not only about beating Donald Trump, the most dangerous president in modern American history.

"Our campaign is about transforming our country, and creating a government based on the principles of economic, social, racial and environmental justice."

77-year-old Sanders is not a member of the Democratic party in the Senate, but he often aligns with them.

He joins what's becoming an increasingly crowded field of candidates seeking the 2020 Democratic nomination.

At least four other senators - Kamala Harris, Cory Booker, Elizabeth Warren and Amy Klobuchar - are formally seeking the nomination.

Senator Kirsten Gillibrand has also announced an 'exploratory committee', a key first step for potential candidates.

Sanders is a high-profile progressive, and joins the race alongside several other left-leaning and liberal politicians - such as Senator Warren and Hawaii Congresswoman Tulsi Gabbard.