(Reuters) – The U.S. Coast Guard is leading a search for two Marine helicopters with a total of 12 people on board that collided near the island of Oahu in Hawaii, officials said on Friday.

The CH-53E helicopters, belonging to the 1st Marine Aircraft Wing from the Marine Corps Air Station at Kaneohe Bay, were reported to have collided just before midnight local time, Coast Guard spokeswoman Sara Mooers said.

No survivors have been rescued from the crash more than seven hours after it occurred, said another Coast Guard spokeswoman, Petty Officer Second Class Melissa McKenzie.

“We remain hopeful,” McKenzie said.

Just after midnight, the crew of a Coast Guard helicopter spotted debris in the waters off the town of Haleiwa on the north shore of Oahu, but did not find any of the passengers.

A Coast Guard cutter was on scene and another one was en route and expected to arrive shortly, McKenzie said.

Two U.S. Navy warships have also been sent to join the search, and local police and fire departments were assisting with helicopters, she said.

The initial effort was hampered by dark, cloudy conditions and waves of up to 15 feet, officials said.

The Marine Corps confirmed the search, but provided few additional details.

“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.

(Reporting by Alex Dobuzinskis in Los Angeles and Susan Heavey, David Alexander and Laila Kearney in New York; Editing by Bernadette Baum)