Police in South Australia are searching for the body of a man believed to have been killed by a shark.

On Tuesday morning local time, the 55-year-old was surfing near Granites Beach south of Streaky Bay on the Eyre Peninsula when witnesses reported that he was attacked.

With the assistance of local volunteers, authorities have swept the area by air and water.

In the state this year, there have been three serious shark attacks.

An additional surfer was killed in May about 120km from Streaky Bay, while a third suffered a non-fatal attack earlier this month.

There is no information about the type of shark involved in the attack, but witnesses tell local media that it was over 4m (13ft 1in) long.

Phil McEvoy, who lives in Streaky Bay, told the Australian Broadcasting Corporation (ABC) that he has heard sirens for quite some time.

When the sirens went away towards the back beach area where the surf is, I knew something wasn’t right.

The man was one of six surfers who were in the water at the time, but he paddled out farther than the others.

Currently, the town is seeing an influx of surfers, and Mr McEvoy believes the fishing season might be contributing to an increase in sharks.

Scientists have cautioned that an increase in shark sightings doesn’t necessarily indicate an increase in shark numbers along South Australia’s west coast waters.

Adelaide, the state’s capital, is approximately 700 km (434 miles) away from Granites Beach.