Democrat Pete Buttigieg endorsed Joe Biden for US president on Monday, providing a major boost to the former vice president's White House hopes just one day after the onetime Indiana mayor himself dropped out of the race.

(Photo: AFP)

"I'm delighted to endorse and support Joe Biden for president," Buttigieg said shortly before Biden was to take the stage at a rally in Dallas on the eve of Super Tuesday, when residents of Texas and 13 other states cast ballots for their choice for Democratic nominee.

"I'm looking for a president who will draw out what is best in each of us, and I'm encouraging everybody who was part of my campaign to join me because we have found that leader in vice president, soon-to-be-president, Joe Biden," Buttigieg said, with Biden standing nearby.

"We have politics right now that makes it sound like being loudest is tantamount to being right. We need politics that's about decency," Buttigieg added. 

"That's what Joe Biden has been practicing his entire life."

The two centrists are former rivals in the Democratic nomination battle who are now united in their desire for a moderate candidate to beat leftist Bernie Sanders, a US senator from Vermont.

After three strong showings in the first three early voting states, Sanders is the frontrunner in the race to face President Donald Trump in November.

Biden bounced back with a blowout win Saturday in South Carolina, but the Democratic establishment remains deeply worried about Sanders -- a self-described democratic socialist -- potentially winning the nomination.

Biden acknowledged the "bittersweet" moment for supporters of Buttigieg, whom he described as "a man of enormous integrity."

Biden said Buttigieg "reminds me of my son Beau," who died of cancer in 2015. 

"It's the highest compliment I can give any man or woman."

Biden has earned a string of endorsements since his South Carolina win. 

Senator Amy Klobuchar dropped out of the race on Monday, and her team told AFP she too would endorse Biden.