Eleven Indonesian fishermen were rescued by Australian maritime authorities from a tiny island after being stranded for six days without food or water, but there are fears nine others may have drowned.

Two fishing boats were destroyed last week by Tropical Cyclone Ilsa, one of the strongest storms to hit Western Australia in more than a decade, said the Australian Maritime Safety Authority (AMSA).

The first group of 11 men swam to shore on the remote Bedwell Island, a stretch of sand in the Rowley Shoals, about 300 kilometers west of Broome on the northwestern Australian coast.

The area is known for its deep-sea fishing.

The desperate men survived without food or water for nearly a week before being spotted by an Australian Border Force (ABF) aircraft during a planned surveillance mission, AMSA said, prompting the dispatch of a rescue helicopter.

The second vessel, believed to have been carrying at least 10 others, sunk in the powerful storm, AMSA said.

One survivor spent 30 hours in the water before reaching Bedwell Island. The remaining nine fishermen are feared dead, AMSA said.

CNN affiliate Nine News Australia reported that the survivors were taken to Broome Hospital for treatment.