Senator Bernie Sanders put his campaign for the Democratic presidential nomination on hold on Wednesday after being treated for a blocked artery following chest pains.

At 78, the far-left Sanders is the oldest candidate vying to take on President Donald Trump in 2020 and becomes the first to halt their campaign for health reasons.

“During a campaign event yesterday evening (in Las Vegas, Nevada), Sen. Sanders experienced some chest discomfort,” Sanders’ senior advisor Jeff Weaver said in a statement.

“Following medical evaluation and testing he was found to have a blockage in one artery and two stents were successfully inserted.”

He added that the Vermont senator was talking and in good spirits, and would be resting over the “next few days.”

The campaign said they were cancelling Sanders’ events and appearances “until further notice.”

Rival candidates rushed to wish Sanders a swift recovery.

“Anyone who knows Bernie understands what a force he is. We are confident that he will have a full and speedy recovery and look forward to seeing him on the trail soon,” tweeted Democratic frontrunner Joe Biden.

Kamala Harris said she was “thinking” of Sanders.

“If there’s one thing I know about him, he’s a fighter and I look forward to seeing him on the campaign trail soon,” the California senator wrote on Twitter.

Massachusetts Senator Elizabeth Warren tweeted that she hoped “to see my friend back on the campaign trail very soon.”

Sanders has served in Congress as an independent aligned with Democrats since 1991, first as a representative of Vermont and then, since 2007, as the state’s junior senator.

Earlier this year he was running consistently in second place behind Biden, who is two years younger, in the race for the Democratic Party nomination for president.

Since July he has jockeyed for position with Warren, who recently moved slightly ahead of him in polls in the crowded field.

Both Sanders’ and Biden’s age has been raised as an issue in their candidacies. Trump is 73, while Warren is 70.

Sanders’ health has generally been good for his age, however, and it has been Biden who has had to bat away questions about his stamina and mental sharpness.

In March Sanders gashed his head on a shower door and had seven stitches, but quickly returned to the campaign trail.

Last month Sanders cancelled three events in South Carolina to rest his voice, which had become hoarse.

He sounded raspy during the third Democratic debate and his campaign said it was because of a “vigorous campaign schedule.”

New York Congresswoman Alexandria Ocasio-Cortez said Sanders’ hospitalisation highlighted the rigours of running for office.

“A lot of people don’t understand how crazy hard grassroots campaigning is — for organisers and candidates alike. Rest up, friend. We’re with you!” she wrote on Twitter.

Sanders is currently third in an average of national polls, on 16.7 percent, according to the website RealClearPolitics.

Biden leads on 26.1 percent with Warren second on 24.4 percent.

It was not immediately clear whether Sanders would be fit to appear in the fourth Democratic debate scheduled for October 15 in Ohio. (AFP)