Two tourists trapped on an out-of-service bus in Japan resorted to calling the police for help escaping, the transport company said Tuesday, as the country grapples with a surge of foreign visitors not all have welcomed.

The mishap occurred in the ancient capital of Kyoto last week after the duo hopped onto the bus not realising it was out of service, according to operator West Japan JR Bus Company.

Soon after departure, it became obvious something was wrong: the bus was eerily quiet and its display panels showed no destination.

But when the tourists asked the driver to stop and let them off, their request was ignored.

"Because of the language barrier, they couldn't communicate very well," the company's spokesman told AFP.

With the bus showing no sign of stopping, the tourists resorted to calling police for help.

At the instruction of police, the driver finally pulled over, and the 20-minute ordeal came to an end.

"We will investigate the facts of what happened, and reprimand or re-educate the driver if they were found to be at fault", the spokesman said.

Overtourism is emerging as a headache for many parts of Japan, including tradition-steeped Kyoto, where locals have complained of tourists harassing the city's famed geisha.

A different Japanese town erected a large mesh barrier last month to block views of famous Mount Fuji, in an attempt to deter photo-taking by an ever-growing number of sometimes unruly tourists.