The electric lock was apparently damaged by the monster wave unleashed by the March 11 earthquake, but employees had not noticed before closing up on Friday for a three-day holiday weekend.

"We didn't realise the lock was broken," an employee of Shinkin Bank in the city of Kesennuma told the Jiji Press news agency.

Japan has seen few incidents of looting and theft after the twin disaster, drawing admiration overseas for restraint in the face of appalling adversity.