Sydney - Five helicopters joined the search for two scuba divers who went missing Friday on Australia's Great Barrier Reef off north Queensland.

The two United States citizens, a man and a woman in their 40s who were not a couple, were reported missing when they failed to return to their dive boat an hour after entering the water.

A fixed-wing aircraft and a coast guard boat were leading the search.

Craig Stephen from Mike Ball Dive Expeditions told the national broadcaster ABC that both were experienced divers and were carrying safety equipment. (dpa)