Bangkok: A young Australian man who told police he had spent all his money in the Thai capital's red-light district allegedly robbed a bank wearing a Guy Fawkes mask and goggles on Monday.

The robbery took just 12 seconds and the only word Zachary Cronin, 23, yelled was "Money" as he pointed a toy gun at tellers of a bank on the outskirts of Bangkok, police allege.

A man in a Guy Fawkes mask and sunglasses is escorted by Thai police in Bangkok. Credit:FM. 91 Trafficpro photo

A frightened teller handed over the equivalent of $6600 in Thai baht as bank staff activated a security alarm, they said.

But Mr Cronin was unaware that an off-duty policeman was among customers of the Thanachart bank in Saphan Kwai, police said.