HALEIWA, Hawaii — Rescuers battled winds of up to 23 mph and waves up to 30 feet as they searched for 12 Marines who are missing after two helicopters they were in crashed off Oahu.

The winds and the waves complicated the search, possibly pushing debris beyond the 2 mile search area.

“It makes finding things incredibly difficult,” Coast Guard spokesman Lt. Scott Carr said.

The Coast Guard was notified late Thursday of the crash by a civilian who saw the aircraft flying then disappear and a fireball. Someone else reported a flare in the sky, Carr said. It was not clear if the fireball and the flare were the same.

The Marines were alerted when the CH-53E helicopters carrying six crew members each failed to return to their base at Kaneohe Bay following a nighttime training mission. Hours later, a Coast Guard helicopter and C-130 airplane spotted debris a couple miles off of Oahu.

The search has included Air Force units as well as a Honolulu Fire Department rescue boat and Coast Guard cutters. Two Navy ships, the USS John Paul Jones and the USS Gridley, were also participating with a Navy squadron of SH-60 helicopters.

The Coast Guard was keeping people out of a wide zone that spanned about 30 miles of shoreline, citing danger from debris. The zone extended from the shore to 8 miles off the coast.

National Weather Service meteorologist Derek Wroe said Saturday that the surf peaked Friday afternoon and is slowly declining. However, a high surf warning remains in effect.

A storm about 1,500 miles to the north and northwest of Oahu was sending large swells to the islands, he said.

The transport helicopters were part of the 1st Marine Aircraft Wing at Marine Corps Base Hawaii.

Known as Super Stallions, they are the U.S. military’s largest helicopter, capable of carrying a light armored vehicle, 16 tons of cargo or a team of combat-equipped Marines, according to a Marine Corps website.

The Coast Guard initially reported that the choppers had collided, but Marine Capt. Timothy Irish said Friday that he did not know if the accident was a collision.

The helicopters normally carry four crew members, but this particular flight also carried one or two instructor trainers, Irish said. He did not know if they were teaching the crew or just observing.

Ty Hart, a 21-year-old from Oregon, was in one of the helicopters, the Oregonian reported Friday night. The newspaper said Hart lives on base in Hawaii with his wife.

Hart’s former high school football coach and teacher, Alan Kirby, described Hart as a positive kid who always had a smile on his face and called him a quick learner on the gridiron.

The family of Capt. Kevin Roche believes he was one of the Marines aboard the helicopters.

“We believe the Marines and Coast Guard are doing everything they can to bring Kevin and his fellow Marines home safely, and we are grateful to everyone involved in the rescue,” said a family statement distributed by brother-in-law Anthony Kuenzel in St. Louis.