HONOLULU: High waves expected for the next several days will hamper the search for 12 Marines missing at sea after two helicopters collided near the island of Oahu in Hawaii, US Coast Guard officials said on Friday.

Two Coast Guard cutters and several Coast Guard aircraft were searching, along with two US Navy warships and local police and fire department helicopters, the Coast Guard said.

A safety zone has been set up from the shoreline that matches up with the accident site to 8 miles (13 km) out to sea, the Coast Guard said.

"We've seen debris through the entire area," said Lieutenant Scott Carr, a Coast Guard spokesman.

The CH-53E helicopters, belonging to the 1st Marine Aircraft Wing from the Marine Corps Air Station at Kaneohe Bay, were on a routine training mission when they were reported to have collided just before midnight local time (1000 GMT), Coast Guard spokeswoman Sara Mooers said.

The wide-ranging search for the Marines was hampered by high surf and poor visibility from rain storms.

The rescue effort will continue on sea and air throughout the night, though bad weather will continue to hamper the efforts, said Mooers.

"It does move things around and keeps us busy," Mooers said.

A Coast Guard helicopter crew spotted debris in the water off the town of Haleiwa on the north shore of Oahu but they did not find passengers.

The debris field spanned more than 7 miles off the coast, the Coast Guard said.

"Thoughts & prayers are with our Marines & their families in Hawaii as search efforts continue," General Robert Neller, commandant of the Marine Corps, said in a message on Twitter.

No distress call was issued by either aircraft. Authorities were notified by a man standing on the beach who saw a fireball over the ocean after seeing the helicopters flying in that area, Carr said at a news conference.