A US Army MH-60 Black Hawk helicopter carrying four service members crashed during a routine training mission near Joint Base Lewis-McChord in Washington state late Wednesday, sparking a wildfire and prompting a large-scale emergency response.The Army confirmed the incident in a statement on Thursday, but did not disclose the condition of those on board. The helicopter belonged to the 160th Special Operations Aviation Regiment, known as the “Night Stalkers.” The cause of the crash remains under investigation.“This remains an active, ongoing situation,” the Army said. Army spokesperson Ruth Castro told the Associated Press that the incident was being treated as a search mission, adding that the “most professional and skilled” personnel were handling the response and were fully cooperating with law enforcement.The helicopter went down at around 9 p.m. local time in the Summit Lake area, west of Olympia, according to local officials. The crash ignited a fire that had grown to about one acre by Thursday morning, said the Washington Department of Natural Resources. Crews from multiple agencies, including military units and wildfire staff, were deployed to contain the blaze.Thurston County Sheriff Derek Sanders said deputies reached the crash site but were initially unable to continue rescue efforts because of the fire. “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,” he said on Facebook.Rescue helicopters, including King County’s Guardian 1, and special operations units were also dispatched to the area. Flight-tracking data suggested the Black Hawk’s signal was last detected shortly before 8 p.m., about 2.5 miles east-southeast of Summit Lake.Joint Base Lewis-McChord, which is jointly operated by the Army and Air Force, is about 10 miles south of Tacoma and home to around 40,000 active-duty troops.