Beijing has become more assertive in the area, stoking tensions with rival claimants in Southeast Asia as well as Canberra and Washington -- traditionally the dominant naval and air power in the Asia-Pacific region.

Defence sources told the Australian Broadcasting Corporation that helicopters were targeted during night flights, forcing the pilots to temporarily return to their ship for medical check-ups.

The broadcaster did not detail why the pilots sought check-ups and how exactly the helicopters were targeted.

The laser attacks were believed to have come from fishing boats, but ABC said it was not yet formally confirmed if they were Chinese-flagged vessels.

Analysts have said China operates a maritime militia that includes fishing trawlers to carry out missions in the South China Sea.

Australian warships have been on a months-long engagement mission in Asia that concluded this week.

There was no immediate comment from the defence department.

China claims sovereignty over virtually all the resource-rich South China Sea, despite rival claims from its Southeast Asian neighbours.

The Australian navy has conducted joint exercises in the South China Sea with other nations, including the United States.

Beijing last year rejected US allegations that Chinese nationals shone military-grade lasers at American pilots in Djibouti, where China operates a naval base. Two US pilots suffered minor eye injuries from those lasers, according to the Pentagon.