Minutes after the UH-60 Black Hawk helicopter took off on Thursday afternoon, the Minnesota National Guard crew sent out a dire alert: “Mayday.” Then the signal disappeared.

The Guard lost contact with its helicopter just after 2 p.m. local time, officials said. Its wreckage was found in a field some two hours later. The crash killed all three soldiers on board.

The helicopter left from the Army Aviation Facility in St. Cloud, Minn., about 65 miles northwest of Minneapolis. The journey was a “maintenance test flight,” Guard officials said, but they didn’t disclose any other information about the circumstances of the crash, citing an impending investigation. Authorities have not named the victims.

“My heart breaks for the families, the friends and the fellow soldiers,” Gov. Tim Walz (D) said at a Thursday evening news conference. “The coming days will be dark and difficult.”

Walz, who served for 24 years in the Army National Guard, postponed a holiday tree lighting ceremony in St. Paul and traveled to the scene. He wasn’t a pilot, his spokesman said, but he rode in Black Hawks during his service.

“These are brothers in arms,” he said. “It’s a tough time.”

During the hours the helicopter was reported missing, several state and local agencies swarmed the rural landscape where the craft was believed to have gone down. The fire department in St. Paul sent members of its aviation rescue team after dispatchers broadcast the helicopter’s mayday signal, the department said.

A Minnesota State patrol helicopter spotted the wreckage from above, and authorities converged on the farm near Marty, about 16 miles south of St. Cloud, where the helicopter had crashed into a tree stand.

Aerial footage of the wreck showed a twisted helicopter frame amid downed trees. What appeared to be scorch marks streaked across snow-covered ground.

“Our Minnesota National Guard family is devastated by the deaths of these soldiers,” Maj. Gen. Jon Jensen, the Adjutant General of the Minnesota National Guard, said in a statement. “Our priority right now is ensuring that our families are taken care of.”

The investigation into the crash will be led by inspectors from the Army Safety Center at Fort Rucker in Alabama, officials said. Roads around the crash site will probably be closed for days during the probe, said Chief Deputy Dan Miller of the Stearns County Sheriff’s Office.

At least two onlookers saw the helicopter go down, the Minneapolis Star Tribune reported, but there was no tracking beacon aboard the aircraft, making it difficult to track. The witnesses reportedly said “it went down hard.”

“On behalf of all Minnesotans, we offer our deepest sympathies to the families of these warriors,” Walz said. “They paid the ultimate price in service to Minnesota and to the United States of America. Words will never ease the pain of this tragic loss and the state of Minnesota is forever in the debt of these warriors.”