US Democratic presidential candidates clashed in their latest debate, with front-runner Bernie Sanders criticised over his economic agenda and healthcare plans.

The debate in South Carolina last night was the tenth of the campaign cycle.

Rivals attacked Mr Sanders' ambitious economic agenda and warned his nomination would be a "catastrophe" that would cost Democrats the White House and control of Congress.

In a debate that featured candidates repeatedly shouting over one another and ignoring their time limits, Mr Sanders' opponents united in attacking the self-avowed democratic socialist as a risky choice to face Republican President Donald Trump in November.

"Bernie will lose to Donald Trump, and Donald Trump and the House and the Senate and some of the statehouses will all go red," Mr Bloomberg said, adding that would be "a catastrophe".

Pete Buttigieg, the moderate former mayor of South Bend,Indiana, criticised Mr Sanders for the shifting estimates on the costs of his proposals such as government-run healthcare and warned that the front-runner would bring about chaos.

"I can tell you exactly how it all adds up. It adds up to four more years of Donald Trump," Mr Buttigieg said.

"If you think the last four years has been chaotic, divisive, toxic, exhausting, imagine spending the better part of 2020 with Bernie Sanders versus Donald Trump."

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Mr Sanders, a senator from Vermont, has taken command of the Democratic race after his resounding win last week in Nevada.

The debate was the last chance for his opponents to try to stop his momentum before Saturday's South Carolina primary and next week's 14 vital Super Tuesday contests.

Mr Sanders largely held his ground.

He defended healthcare as a human right and said his economic and social justice agenda, including his Medicare for All plan that would replace private health insurance with a government-run programme, is supported by the American people.

"If you want to beat Trump, what you're going to need is an unprecedented grassroots movement of black and white and Latino, Native American and Asian people who are standing up and fighting for justice. That's what our movement is about," Mr Sanders said.

Underscoring the high stakes of the debate, even Elizabeth Warren, a senator from Massachusetts and a progressive ally of Mr Sanders, took a swing at her old friend.

"I think I would make a better president than Bernie. And the reason for that is that getting a progressive agenda enacted is going to be really hard," said Ms Warren, who is trying to revive her struggling campaign after poor showings in the first three nominating contests.

"I dug in, I did the work, and then Bernie's team trashed me."

Senator Amy Klobuchar, who is seeking to become the moderate alternative to Mr Sanders, but who so far has failed to make an impact, said neither Mr Sanders nor Ms Warren had shown the leadership in the Senate to accomplish much.

"It matters if you can actually get things done," she said.

Mr Bloomberg, who turned in a shaky performance in his debut debate last week in Nevada, was sharper and more aggressive this time.

He defended his treatment of women after Ms Warren reprised attacks on what she said was his history of making sexist comments.

He said he complied with a request from Ms Warren in the last debate to release three women he worked with from their non-disclosure agreements.

"The trouble is, with this senator, enough is never enough," he said. "We did what she asked, and thank you, you've probably made the world better because of it."

Mr Bloomberg, who has been bankrolling a massive advertising blitz, said he also spent his own money to help elect nearly two dozen Democratic House of Representatives candidates in 2018 and "put Nancy Pelosi in charge" so Congress could "control" the president.

He also took aim at Mr Sanders, referring to reports that US intelligence officials believe Russia is trying to help Sanders in the election.

"Vladimir Putin thinks that Donald Trump should be president of the United States, and that's why Russia is helping you get elected so you lose to him." 

Mr Sanders responded: "Hey Mr Putin, if I'm president of the United States, trust me you're not going to interfere in anymore elections."

Mr Sanders was criticised for his recent comments praising aspects of the late Cuban revolutionary leader Fidel Castro's leadership, but said he opposed authoritarianism all over the world.

"When dictatorships - whether it is the Chinese or the Cubans - do something good, you acknowledge that. But you don't have to trade love letters with them," he said.

Mr Sanders, who is Jewish, also drew the anger of the American Israel Public Affairs Committee (AIPAC) lobby group and its supporters over the weekend when he said he would skip its meeting, labeling it a platform for "bigotry".

During the debate, he said Israeli Prime Minister Benjamin Netanyahu was "a reactionary racist".

The pressure for a strong performance was high for all of the contenders.

Joe Biden, the national front-runner not so long ago, needs to win South Carolina to keep his campaign alive and said he expected to finish first on Saturday.

The former vice president has been counting on his traditional strong support from black voters, who make up about 60% of the Democratic electorate in the state, but the latest Reuters/Ipsos poll showed Mr Sanders surpassing Mr Biden in support among the critical constituency.

"I'm here to earn it. But, folks, I intend to win in South Carolina, and I will win the African-American vote here in South Carolina," Mr Biden said.