A PILOT was lucky to escape unharmed after a light plane crashed off the runway at Bankstown Airport today.

The crash came as parts of Sydney was blanketed in heavy fog, forcing the temporary cancellation of ferries and causing traffic chaos.

Emergency crews were called to the airport about 7.30am after a twin engine aircraft skidded off the runway following a mishap on take-off.

The plane finished bogged in mud and grass before the pilot climbed free, unhurt.

Bankstown Airport spokeswoman Meredith Laverty said it was unclear what caused the crash.

The airport was blanketed in light rain, but there was no indication conditions played any role in the mishap.

The accident forced the closure of one runway, however, the airport remained operational.

"We are recovering the aircraft at the moment...just moving it to a safer spot," she said.