The fate of 12 Marines remains unclear after two U.S. military helicopters apparently collided and went missing off the coast of the Hawaiian island of Oahu late on Jan. 14, the U.S. Coast Guard said.

Marine Maj. Christian Devine told CNN that the Coast Guard was searching for survivors. A fire and a debris field, including an empty life raft, had been discovered about 2.5 miles north of Haleiwa Beach, Coast Guard Chief Petty Officer Sara Mooers added.

Debris field drifted 8 miles

Rescue efforts are apparently complicated by the fact that by the morning hours of Jan. 15, the debris field had drifted about eight miles offshore, leading to a search area that is about 6 miles offshore and spans about 11 miles along the shoreline, Hawaii News Now reported.

"Anytime you are dealing with a debris field ... that's pretty normal that it will move," Coast Guard Lt. Scott Carr explained in an interview with the local channel. "As you go over time in any search and rescue, the area typically starts to get bigger."

The Coast Guard's rescue operations had begun when U.S. Marine Corps officials reported the missing aircraft around 11 p.m. on Jan. 14, CNN noted. A Coast Guard helicopter was dispatched to the incident site shortly after midnight.

Choppers have long, troubled history

The helicopters involved in the apparent collision are two Sikorsky CH-53 Sea Stallion, which the U.S. military has used since the mid-1960s. Due to the aircraft's large size and troop capacity, the choppers have been involved in a large number of aerial accidents during their operational history.

Last month, two Army pilots from Fort Campbell were killed when their AH-64D Apache helicopter crashed during a routine exercise, ABC News recalled. And in March 2015, 11 veteran Marines and soldiers lost their lives when their UH-60 Black Hawk helicopter crashed during a training mission off the coast of Florida, the network added.

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