(Reuters) - A mouse caused a big delay for a flight from London to San Francisco, forcing passengers to switch aircraft after the tiny stowaway was discovered.

The mouse was spotted scurrying under a door aboard British Airways Flight 285 at London's Heathrow Airport on Wednesday as passengers were buckled in for departure, a passenger told San Francisco television station KGO.

This forced them to switch aircraft and endure a four-hour delay, according to KGO.

Some passengers joked that the mouse lacked a visa to enter the United States, according to passenger Annina Salven, who laughingly told KGO it made sense to switch planes "because I really wouldn't want to eat food on a plane that had a mouse."

Rodents have been known to chew through the wiring on aircraft, with potentially dangerous results.

British Airways in a statement confirmed the disruption of its Flight 285 from London's Heathrow Airport to San Francisco, saying "on this occasion there was one very small customer who we had to send back to the gate."

(Writing by Alex Dobuzinskis; Editing by Patrick Enright and Cynthia Osterman)