US military officials said they located the crash site of a missing Marine helicopter in the California mountains.
The fate of the five Marines travelling on board is unclear, but officials said the rescue operation is ongoing after they were “reported overdue”.
The Marines were on a training flight to Marine Corps Air Station Miramar, near San Diego, early on Wednesday.
The crashed helicopter, a CH-53E Super Stallion, was found about 45 miles from its destination.
The Marine Corps said the missing Marines were assigned to Marine Heavy Helicopter Squadron 361, part of the 3rd Marine Aircraft Wing which is headquartered in Miramar.
A Marine Corps spokesperson told the BBC that more information would be forthcoming about the status of the five Marines who were on board at the time of the crash.
Fire crews were alerted to the missing aircraft at 02:20 local time on Wednesday (10:20 GMT). Crews were dispatched to an area near Lake Morena, California, before locating the aircraft hours later – less than 15 miles away (24km) in Pine Valley.
Rescuers were “using ground and aviation assets to locate the aircrew in coordination with the San Diego County Sheriff’s Department and multiple federal, state and local agencies”, The 3rd Marine Aircraft Wing said in a statement.
The search efforts have been hindered by heavy snow and wintry conditions in the area, officials said. The incident came as the area was experiencing a winter storm that has included heavy rains and several inches of snow in mountainous areas.
First introduced to active service in 1981, the CH-53E Super Stallion is considered a mainstay of Marine Corps aviation and usually serves in a transport role. It can carry up to 37 passengers in its normal configuration.
In addition to carrying troops, the helicopter – which is also used by the US and Japanese navies – can be used in combat and to transport supplies.
The Marine Corps Super Stallions also has a checkered safety record. There have been several serious accidents involving the helicopter in recent years.
In April 2018, for example, four troops were killed when their Super Stallion crashed near El Centro, California while on a training mission.
In a separate incident in January 2016, 12 Marines were killed when two Super Stallions collided over the Pacific near Oahu in Hawaii.
This also is not the first accident to occur in these California mountains recently.
In August, a Marine Corps pilot was killed when his F/A-18 Hornet jet crashed in an area similarly near to the Marine Corps Air Station Miramar.