DETROIT (AFP) - US Democratic presidential front runner Joe Biden told a Detroit factory worker he was "full of s**t" in a heated exchange on gun control Tuesday (March 10) as he campaigned in Michigan's crucial primary.

Footage shared by reporters - and amplified by rival Bernie Sanders's camp and supporters of President Donald Trump - showed the former vice-president confronted by the worker in a hard hat and reflective vest at an under-construction Fiat Chrysler plant.

The man can be heard accusing Biden of "actively trying to diminish our Second Amendment right and take away our guns".

Biden immediately shoots back: "You're full of s**t. I support the Second Amendment," adding that he has his own 12-gauge shotgun.

"You're not allowed to own (just) any weapon. I'm not taking your gun away at all," Biden went on.

The worker then claims Biden had said in a viral video he was going to take guns away.

"I did not say that! I did not say that!" Biden counters, raising his voice as the tone of the exchange becomes more terse and adding that the video was "like the other ones that came out" that were "lies."

The back-and-forth continued until the worker was pulled away by a union leader.

Biden was hoping to deal a debilitating blow on Tuesday to leftist rival Bernie Sanders as Michigan and five other states vote in the Democratic presidential primaries for a nominee to take on President Donald Trump in November's election.

Barack Obama's former deputy has drawn criticism for previous colourful and head-scratching exchanges on the campaign trail.

In February, he was caught on camera calling a young woman a "lying, dog-faced pony soldier" - apparently a joke drawn from John Wayne's movies.