Media playback is unsupported on your device Media caption Jeb Bush: "You should be showing up to work"

US Republicans have traded blows in a heated presidential debate in Colorado that featured several angry exchanges.

Frontrunners Donald Trump and Ben Carson, with no political experience, were under attack from the start.

Ohio Governor John Kasich condemned their "fantasy tax plans" and added: "We can't elect someone who doesn't know how to do the job."

Mr Carson, a retired neurosurgeon who has edged past Mr Trump in national polls, had a quiet night in Boulder.

His tax proposal, which is based on biblical tithes, was decried by Mr Kasich, who also dismissed Mr Trump's plan to deport 11 million undocumented immigrants and build a wall on the Mexico border.

Political friendships were strained by some of the testy exchanges, notably one between former Florida Governor Jeb Bush and Florida Senator Marco Rubio.

Mr Bush urged Mr Rubio, once his protege, to resign from the Senate because of his poor voting record.

He mocked his younger Florida rival by asking him if he was working the "French working week".

Do the French really work less?

The five key confrontations

The media were also in the firing line - Texas Senator Ted Cruz got the night's biggest applause when he attacked the hosts, CNBC for stirring confrontation.

"The questions that have been asked so far in this debate illustrate why the American people don't trust the media. This is not a cage match."

The hostility against CNBC continued after the debate when Republican National Committee chairman Reince Priebus complained about the "gotcha questions".

Analysis - Nick Bryant, BBC News, Boulder

Twin contests played out on the stage in Colorado - a fight to become the candidate of the Republican establishment and a battle to become the standard bearer of the radical right.

In the first contest, Jeb Bush delivered another listless performance that will deeply worry his donors, and a premeditated decision to attack his friend and rival Marco Rubio for absenteeism from his day job as the Florida senator backfired badly. It seemed so contrived, as Rubio, a big winner tonight, deftly pointed out.

In the establishment contest, it was the defining exchange of the night, and will enhance Rubio's growing stature and further diminish Bush. The New Jersey Governor Chris Christie also outstripped Bush.

As for a rumble in the Rockies between Donald Trump and the candidate who dislodged him in the polls, Ben Carson, it never unfolded. Trump was low-key - it seemed almost that he is tiring of the process. Carson disappeared for much of the debate.

Perhaps sensing a chance to impose himself, the Texas Senator Ted Cruz delivered an impassioned attack on the moderators of the debate and the media more broadly for its liberal bias. Speaking of his born-again father will have impressed evangelicals. This was the best two hours of the Cruz campaign so far.

But the main headline of the evening comes from Jeb Bush. He needed to energise his troubled campaign tonight, and he failed abysmally.

Media playback is unsupported on your device Media caption Mr Kasich decried the "fantasy" tax plans of rivals

Image copyright Getty Images Image caption Donald Trump (middle) and Ben Carson (right) were eclipsed by Marco Rubio (left)

Image copyright Reuters Image caption Ten candidates took the stage

Other highlights included:

Mr Trump denied his economic plan was a "comic-book version" of a presidency campaign

Mr Rubio touted his humble upbringings and said he would fight for struggling Americans

New Jersey Governor Chris Christie said the government "stole" Social Security taxes

Mr Trump called gun-free zones "target practice" for the mentally ill

he denied calling Mr Rubio the "personal senator" of Facebook founder Mark Zuckerberg, although the description is on his own website

Carly Fiorina accused Democratic candidate Hillary Clinton of hypocrisy because every single policy of hers is "bad for women"

The four lowest-polling Republican candidates squared off in an early debate.

Lindsey Graham, a senator from South Carolina, got the most laughs, especially when he said Democratic candidate Bernie Sanders "went to the Soviet Union on his honeymoon and I don't think he ever came back".

Primary voting begins in February in Iowa, 10 months before the nation goes to the polls to vote for its new president.