Three rescued after boat flips off Sydney

Three men whose boat capsized in rough seas off Sydney have been rescued thanks to a bushwalker's keen eye.

The walker saw the men in the water near Wedding Cake Rock in Sydney's south on Wednesday and called for help, sparking a rescue involving three helicopters.

The men had been in the water for about an hour before being spotted, NSW Ambulance Inspector Andrew Bibby said.

"All agencies worked well together to coordinate the rescue, with the men winched from the water and taken to NSW Ambulance paramedics to be assessed," Mr Bibby said.

The men were treated for hypothermia at Wattamolla Beach before being taken to Sutherland hospital in a stable condition.

Mr Bibby said the use of life jackets was key in preventing a more serious outcome.

"This is a timely reminder to anyone heading out on the water to be prepared," he said.

Marine Rescue NSW said boaters should ensure to bring an emergency beacon, called an EPIRB, when heading out on the water, particularly more than two nautical miles.

The beacon emits a continuous radio signal when activated, alerting search and rescue services.

A spokeswoman for NSW Police confirmed the overturned boat has been safely towed to shore.

Also on Wednesday, firefighters were called to a boat fire at Wollongong Harbour, where a fishing trawler had ignited on the water.