TOKYO (AFP) - A hapless armed robber in his 60s broke his leg while holding up a convenience store in Japan and had to use the shop's payphone to call an ambulance, according to a report and police.

The inept thief tussled with a 35-year-old store clerk after threatening him with a knife in Chiba, east of Tokyo, on Sunday.

The crook was disarmed in the struggle, which saw him fall to the ground and break his leg before hobbling out of the shop, the local China Nippo newspaper reported.

In increasing pain and unable to get very far, the unnamed man limped back an hour later and used the payphone at the store to call an ambulance, the newspaper said.

Detectives are planning to arrest the suspect when he is released from hospital, according to the report.

"A man in his 60s is being treated at the hospital he was taken to," a Chiba police official told AFP. "As the victim took the knife away, the suspect could not achieve his purpose," the official said.