A large great white shark has forced swimmers from the water during WA's Rottnest Channel Swim.
About 100 people were pulled from the water on Saturday after a competitor saw the predator, estimated at three to four metres long, swim beneath him.
Organisers enacted a risk management plan and evacuated anyone within a 1km radius.
Helicopters flew above after the sighting to monitor the situation.
More than 2500 people participated in the annual event, with ex-Premier Colin Barnett sounding the starting horn.
A support boat was towed after it began to sink about 8km in, with five people pulled on to a rescue vessel, Fremantle Sea Rescue tweeted.
Solomon Wright took out the solo men's title and set a new record of 3:59:28, shaving 47 seconds off the previous time from 2000.
"I'm happy with the win, the record is just the cherry on top," he told Perth Now.
Olympic swimmer Heidi Gan was the fastest solo female swimmer, with a time of 4:21:55.
A total of 220 did not finish the race, including those pulled from the water.
The event is a 19.7km open water swim from Cottesloe Beach to Rottnest Island.
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