A fisherman has been pulled from shark-infested waters off the coast of Western Australia, after treading water for 20 hours when his boat sank.

The man was spotted by a local news station's helicopter on Friday, with at least one hammerhead shark circling 20 metres away.

He was eventually picked up by a rescue boat and was taken to Royal Perth Hospital suffering from exposure and hypothermia.

The fisherman was with two other men, one of whom did not survive, while the other is still missing.