SYDNEY, June 3, 2009 (AFP) - Three lucky backpackers were plucked from shark and crocodile infested waters off the coast of Australia by rescuers who stumbled on the stricken trio after their boat sank, officials said Wednesday.

The tourists, who have not been identified, were three kilometres (nearly two miles) off the coast of the northern Australian city of Darwin on Tuesday when their small boat capsized in choppy seas during a fishing trip.

But the backpackers were saved by chance when a customs boat searching for a missing vessel happened to spot their heads bobbing in the water just 30 minutes after the accident.

"They came across their heads in the water completely by accident," said Ian Badham from the aerial rescue service Careflight.

"Now it's very unlikely they would have been found any other way, so those three people, they've just won lotto," he said.

Darwin harbourmaster Captain Bruce Wilson said two men and a woman, including a French citizen and a Filipino, had been hauled out of the water after customs officers spotted them at sea.

The trio did not have a radio or flares, and nobody would have known that they were in the water, which he said.

"It would have been like looking for a needle in a haystack," Wilson said. "It really was lucky because the Corio Bay (customs vessel) was doing a search, it was daylight, and they were near a shipping channel."

Wilson said that although the water wasn't cold, the trio were still in danger from the deadly creatures that frequent Darwin's harbour.

"Whether you freeze or get chomped by a croc, I don't know which one you'd prefer," he said.