Biden says nuclear "Armageddon" higher since Cuban missile crisis

US President Joe Biden has said the world is facing the biggest threat of nuclear "Armageddon" since the days of President Kennedy and the Cuban Missile Crisis.

Speaking at a Democratic Party fundraiser in New York on October 6, his "off camera" comments were overheard by journalists from the White House pool, per Sky News.

It comes as Russian officials warned of the possibility of using tactical nuclear weapons after suffering huge military setbacks in the invasion of Ukraine.

Describing Russian President Vladimir Putin, President Biden said he had "got to know the guy pretty well".

"He's not joking when he talks about the use of tactical nuclear weapons or biological or chemical weapons because his military is you might say significantly underperforming," Biden said.

And he made clear his concerns that if such weapons were deployed it would quickly escalate into world nuclear conflict.

"First time since the Cuban missile crisis, we have a direct threat of the use nuclear weapon if, in fact, things continue down the path they are going," he said.

"I'm trying to figure out what is Putin's off-ramp?" he said. "Where does he find a way out? Where does he find himself in a position where he not only loses face but loses significant power within Russia?

"We have not faced the prospect of Armageddon since Kennedy and the Cuban missile crisis."

He added: "I don't think there's any such thing as the ability to easily (use) a tactical nuclear weapon and not end up with Armageddon."

During the 1962 crisis, the United States under President John Kennedy and the Soviet Union under Nikita Kruschev came close to using nuclear weapons over the presence of Soviet missiles in Cuba.