Swedish air operator SAS on Tuesday cancelled a flight from Stockholm to Chicago because of an unruly passenger -- a mouse.

The rodent was spotted ahead of boarding on the 08:15 a.m. GMT flight but evaded the many mousetraps laid to catch it, SAS said.

Company spokesman Anders Lindstroem said: "For safety reasons, you don't board when there's a mouse on board.

"We hope to find it overnight," he said, adding that the 250 passengers on the Airbus A330 flight had been understanding.

Apart from disturbing passengers, a mouse on board a flight is a potential danger as it could creep in amongst cables, Lindstroem said, adding that a complete inspection would be carried out once the mouse was caught.

The spokesman said it was the first time a mouse had been discovered on an SAS plane.