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 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.

As he fled, the policeman and a security guard gave chase, they said.

But Mr Cronin's choice of getaway route allegedly turned out to be a dead end street.

He was grabbed with the money in a bag, police said, and was taken to a police station for questioning.

Police Lieutenant Sanit Mahatavorn said Mr Cronin told police he had spent all his money during a month staying in Bangkok's Nana red-light district and wanted money to buy an air ticket home to Australia.

Lieutenant Sanit said Mr Cronin had observed the bank two days previously and chose it because it was usually not busy during morning hours.

He had taken an overhead train to the bank.

Police later escorted Mr Cronin back to the bank where they say he re-enacted the robbery.

Mr Cronin, who was identified as Australian by his passport, has been charged with robbery, a crime which carries punishment of up to 10 years jail in Thailand.

Police have informed the Australian embassy of the arrest and asked it to check on Mr Cronin's background.

No date has yet been set for his court appearance.