Sept. 18 (UPI) — The status is unknown for four special operations soldiers aboard a U.S. Army Black Hawk helicopter that crashed Wednesday evening in Washington state.

The Thurston County Sheriff’s Office said deputies were dispatched to respond to the crash in the Summit Lake, Wash., area and had located the scene of the crash.

The local sheriff told USA Today that “the scene is on fire,” with about an acre burned following the crash that occurred at about 9 p.m. PDT.

The four soldiers are assigned to the 160th Special Operations Aviation Regiment, according to the U.S. Army Special Operations Command.

The crew was on a “routine training flight” when air traffic controllers lost contact with them, which suggested something had gone wrong, a U.S. Army spokesperson told ABC News.

The accident’s cause is under investigation.

Thurston County Sheriff Derek Saunders said the crash site is about 15 miles from Joint Base Lewis McChord.

“Deputies have located the crash site but have been unable to continue rescue efforts as the scene is on fire and is starting to overheat their footwear,” Saunders said. “Special operation rescue units are responding.”

Joint Base Lewis-McChord is located in the Puget Sound region and is home to I Corps and the 62 Airlift Wing. According to the base’s website, there are 40,000 active-duty troops at the base, plus their families and thousands of contractors.

The Military Times reported that the weather was good at Olympia Regional Airport on Wednesday night, with clear skies and a visibility of 10 miles.

This is a breaking news story. Check back for developments.