Actor Zach Galifianakis stunned American TV viewers when he lit up a joint and started smoking it during a political chat show.

The Hangover star was making a point about the upcoming vote for marijuana legalisation on Real Time With Bill Maher when he took the roll-up cigarette and a lighter out of his jacket pocket.

He said: 'It's a tricky thing politically to jump on that bandwagon because I think that maybe people still see it as taboo.'

Galifianakis then started puffing away and offered the joint to fellow guest Margaret Hoover, a conservative news reporter, who smelled the cigarette and verified it was the real thing.

The actor,who was on the show to promote his new film Due Date continued smoking as the political debate on the show continued.

It is believed to be the first time anyone has smoked marijuana live on US TV.