Great Barrier Reef
The planes dropped their payload of 500lb bombs in a marine park off the coast of Queensland after a training emergency

US fighter jets dropped two 500-pound bombs on Australia's Great Barrier Reef after a training exercise went wrong, it has emerged.

Two AV-8B Harriers launched from aircraft carrier USS Bonhomme Richard each jettisoned an inert bomb and an unarmed explosive bomb in the World Heritage-listed marine park off the coast of Queensland state on Tuesday, the US 7th Fleet said in a statement on Saturday.

The four bombs were dropped in more than 50 metres of water away from coral to minimise possible damage to the reef, the statement said. None exploded.

The jets from the 31st Marine Expeditionary Unit had intended to drop the ordnance on the Townshend Island bombing range but had to abort the mission when controllers reported the area was not clear of hazards.

The pilots conducted the emergency jettison because they were low on fuel and could not land with their bomb load, the navy said.

The emergency happened during a joint training exercise known as Talisman Saber, involving US and Australian military personnel.

The Great Barrier Reef is the world's largest coral structure, rich in marine life and stretching for more than 1,500 miles along Australia's eastern coast.

The US Navy and Marine Corps were working with Australian authorities to investigate what had happened, the navy said.