It's emerged that two American fighters jets dropped four bombs on Australia's Great Barrier Reef Marine Park.

They were supposed to be used during a training exercise at the Townshend Island bombing range but the pilots took emergency action after being told the target wasn't clear.

The pilots claim they tried to minimise the damage by releasing the devices over deep water and away from coral reefs.

Although the bombs did not explode, its yet to be determined if any environmental damage was caused.

The Defence Forces are now working with Australian authorities to investigate the incident.