United States Congressman Lee Zeldin has allegedly been attacked during a campaign speech in upstate New York, according to the local sheriff's office.

The Republican member from New York's First District claimed his alleged attacker tried to stab him, but he managed to fend him off.

Mr Zeldin is running for state governor — against Democratic incumbent Kathy Hochul — in November's election.

He was addressing a crowd in the town of Perinton at about 8pm on Thursday, local time, when a 43-year-old man later identified as David Jakubonis climbed the stage and allegedly attempted to attack Mr Zeldin, according to a statement from the office of the Monroe County sheriff.

The attacker allegedly "had a weapon in his hand, swung it towards Mr Zeldin's neck, and told him, 'You're done'," the statement said.

"Members of the crowd and Mr Zeldin's campaign restrained the male until deputies arrived and took him into custody. There were no injuries."

Footage of the attack posted online showed Mr Zeldin, a former soldier, speaking in front of a military helicopter at a veterans' centre, on a stage decorated by hay bales.

The attacker, wearing shorts, a T-shirt and a baseball cap, approached slowly and got within touching distance of Mr Zeldin before the candidate or his team recognised anything was awry.

When the attacker made a swing for Mr Zeldin, the pair grappled for a few seconds before people nearby intervened.

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"Someone tried to stab me on stage during this evening's rally but, fortunately, I was able to grab his wrist and stop him for a few moments until others tackled him," Mr Zeldin wrote on Twitter.

The father of two, a staunch ally of former president Donald Trump, said he was "OK" after the attack.

He was also among the Republicans in Congress who voted against certifying the 2020 election results.

"Relieved to hear that Congressman Mr Zeldin was not injured and that the suspect is in custody," his rival, Ms Hochul, wrote on Twitter.

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"I condemn this violent behaviour in the strongest terms possible — it has no place in New York," added the incumbent, who replaced former governor Andrew Cuomo last year after he quit over sexual harassment allegations.

The sheriff's office said Mr Jakubonis had been charged with attempted assault in the second degree and was released on bail.

AFP/AP