Donald Trump has rocketed to a new high in a poll of likely Republican primary voters, scoring a clear majority at the national level for the first time as key states including Ohio and Florida vote.

A poll from The Economist and YouGov found the billionaire front-runner has the support of 53 per cent of the GOP's voting electorate, up nine points in the last three weeks.

Texas Sen. Ted Cruz is in a distant second place nationally with 22 per cent. Ohio Gov. John Kasich and Florida Sen. Marco Rubio have 11 and 10 per cent, respectively.

The astonishing numbers indicate that Trump no longer has a 'ceiling' of support that's too low for him to win over most Republican voters.

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FLYING HIGH: Donald Trump has hit 53 per cent in a new poll of likely Republican primary voters

TRUMP TRAIN: The Donald's numbers (in green) are taking off, in part because of Dr. Ben Carson's exit from the White House race

CRASHING TO EARTH: Florida Sen. Marco Rubio is in last place with just 10 per cent nationally

They also suggest a major enthusiasm gap between Trump and his Republican rivals.

Among all Republicans, Trump scores just 32 per cent. The next highest categery is self-identified GOPers who have 'no preference.'

But when the numbers are limited to only those Republicans who have voted in primary elections – or plan to – the billionaire front-runner opens up a colossal lead.

Much of Trump's bump in the YouGov poll came from Dr. Ben Carson's exit from the race, as the former candidate's supporters flocked to The Donald. Carson endorsed Trump on Friday.

Trump has also edged past Kasich in the all-important favorability category, with 66 per cent of likely GOP primary voters saying the have a positive impression of him.

That compares with 63 per cent for the more restrained and pleasant-talking Ohio governor.

THEY LIKE HIM: About two-thirds of Republican primary voters now have a favorable impression of Trump, putting him at the top of the GOP field

SUPPORT: Most Republican voters believe the party elites should get behind Trump, and believe he's ready to be commander-in-chief of the U.S. armed forces

Among the party faithful, Rubio is the least-liked of the remaining four Republican candidates, with favorable ratings from 53 per cent.

Trump's positive numbers are weaker among Americans in general – including Democratic partisans – with 61 per cent saying they have an unfavorable opinion of him.

The new poll took the Republican electorate's pulse on the thorny question of whether the GOP 'establishment' should support Trump if he wins enough convention delegates to become the party's nominee.

An overwhelming 75 per cent said party elites should get behind him.

EATING DONALD'S DUST: Ohio Gov. John Kasich (left) and Texas Sen. Ted Cruz (right) are nowhere near Trump's national poll numbers among likely Republican primary voters

MAKE GLOATING GREAT AGAIN: Trump boasted his new poll numbers on Facebook

More than anything else, pollsters found, Trump's broad support is due to his willingness to avoid being 'politically correct.'

Thirty-nine per cent of his backers chose that reason over his success in business and his policies on immigration, taxes and trade.

And fully half of Republicans who support another candidate say it's The Donald's politically incorrect, plain-talking style that makes him appealing.

Most of the survey's respondents spoke to pollsters before the past weekend's series of quasi-riots, violent protests and arrests at Trump rallies in Illinois, Missouri and Ohio.

But 74 per cent of Republican primary voters say they expect him to be the party's presidential nominee.

Six in ten say Trump cares about people who are like them. The same number believe the real estate developer cares more about the country than about himself.