That's it from police for the time being.
We'll continue to bring you updates on the search today on ABC News.
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One person dies, search underway for two missing after fishing boat found upturned near Port Lincoln
The State Emergency Service are involved in the search. (Supplied: Mark Thomas)
A body has been recovered from the water and two people are still missing after a fishing boat with five people onboard capsized near Port Lincoln on South Australia's Eyre Peninsula.
Two survivors — a 44-year-old man and a 13-year-old boy, both from the Adelaide suburb of Torrens Park — were found on a reef and winched to safety in the early hours of this morning, but aerial and ocean searches for the two others are ongoing.
Family raised the alarm about 8:30pm on Monday night when the boat failed to return from a fishing trip, and police found the upturned and damaged vessel around 2am this morning near Spilsby Island in Spencer Gulf.
"A short time ago we located a deceased person in the water in the same location," Superintendent Paul Bahr said on Tuesday morning.
"That person is now currently being conveyed back to Port Lincoln by the State Emergency Service and obviously we will be conducting inquiries on behalf of the coroner in regard to that death.
"At this stage we don't know who that person is, they're yet to be identified."
Live Moment
Police are searching for three people missing off the coast of Port Lincoln after their boat capsized overnight.
Police said after being winched to safety, the two survivors were taken to Port Lincoln Hospital for treatment for non-life-threatening injuries including hypothermia.
The pair have told them the boat was swamped by a wave around 4pm yesterday, overturning it and throwing the people onboard into the water.
"We're still talking to the survivors, so we're still trying to put that picture together in terms of how they ended up on the reef away from the boat," Superintendent Bahr said.
Police said those onboard were a group of family members and close friends.
The search is continuing for the two people still missing.
"One of the things we do in all these sorts of cases is we map drift patterns," Superintendent Bahr said.
A large sea and aerial search is underway after a fishing boat carrying five people overturned in the Spencer Gulf. (ABC News)
"That drift pattern is dictating where the search is. Currently we have a further police helicopter in the air, we have other boats in the water, and they're continuing the search."
Police Water Operations Unit, the local sea rescue squadron, a PolAir helicopter and a Challenger aircraft from Australian Search and Rescue have been deployed in the area.
'No radio distress call'
Police said the capsized vessel had been recovered and was being brought to shore by another fishing boat.
Superintendent Bahr said the boat left Billy Lights Point at Port Lincoln yesterday morning.
Superintendent Paul Bahr said a man and a teenage boy have been rescued off a reef near Spilsby Island. (ABC News: Jodie Hamilton)
Tumby Bay resident Erica Larwood told ABC Eyre Peninsula she was out on a morning walk at about 6am when she saw what she suspects was a flare.
"It lasted for a little bit then it disappeared, so we were a little bit concerned and just kept walking up along the foreshore at Tumby and then we got up near the hospital and saw another one," Ms Larwood said.
She called the SES to notify them of the two flare signals.
"Better to do something than nothing," she said.
The search is being assisted by local fishing vessels. (ABC Eyre Peninsula: Jodie Hamilton)
After the alarm was raised by family last night, police immediately checked local boat ramps before commencing aerial searches, but said they were not aware of distress calls from the boat.
"We received no EPIRB activation, no radio distress call, no flares were sighted, and from what the survivors have told us it would be highly unlikely there would have been time to have activated any of that," Superintendent Bahr said.
"The reports we're getting back from the boats in the search area are that the conditions are quite calm. There is a swell, about a 1.5-metre swell."
The Pacific Explorer, a cruiseliner that has more than 2,400 guests onboard, was diverted to help, a P&O Cruises spokesperson said.
It left Adelaide last night and was due to arrive in Port Lincoln on Tuesday morning as part of its three-day voyage.
A boat out searching for people missing from a capsized fishing boat near Port Lincoln. (ABC News)
Local fisherman, Greg James, said swells on Monday evening were about 15 knots and "a cross flow of swells" could be dangerous around Spilsby Island.
"You got very deep water becoming very shallow on the northern end of Spilsby where there's a big sandy spit that runs quite a few metres north of the island," he told ABC Radio Adelaide.
"My thoughts are certainly with those guys."