Seven boats from the Sydney to Hobart yacht race diverted to the scene of a light plane crash off the south-east coast of Tasmania as they neared the finish on Monday night.

Two people – the pilot and one passenger – were on board the aircraft, a Cessna 172 (VH-PFT), which had been conducting aerial photography of the race.

Search crews found an oil slick in south-east Tasmanian waters late on Monday night, but were unable to locate the plane or people on board.

"At this stage of the search, neither the pilot nor the passenger have been found," police said.

Aerial sweeps by helicopters have been suspended and will resume at first light on Tuesday.