Canadian Prime Minister Mark Carney said Sunday that four service members were killed and dozens more seriously injured in a fire at a military base in Alberta, describing it as one of the worst peacetime tragedies for Canada's military on domestic soil.

The blaze broke out Saturday during a training exercise at Canadian Forces Base Wainwright, and fire crews scrambled late that night as fierce winds whipped flames beyond the base and into the surrounding rural area. The Canadian military said Sunday there were no indications the incident was the result of terrorism, but the cause remained under investigation.

Speaking in a televised address, Carney said the families of those killed had been notified and that the situation was still evolving. He said the service members who died and those who were injured had been participating in military training when the fire broke out. Flags would fly at half-staff on federal buildings across the country in honor of those affected by the tragedy, he added.

Carney said those affected included reservists and soldiers from Princess Patricia's Canadian Light Infantry, one of Canada's most storied military regiments. The personnel had come from bases across the country to train at Wainwright.

It was not immediately clear exactly how many people had been injured. Carney said the wounded were being treated in Wainwright, Edmonton, Red Deer and Calgary.

Cathy Keane, a mayoral candidate in Ontario, said her eldest son was among the military personnel critically injured. "As a mother, right now I need to be with my son and family," she wrote on Facebook, saying she was traveling to Alberta.

In Edmonton, roughly kilometers (112 miles) northwest of the base, a hospital doctor told Canada's national broadcaster that patients were taken to hospitals across the city as health care facilities around the base became "completely overwhelmed" by the number of people needing care.

"This number of patients would overwhelm the city of Edmonton," Dr. Warren Thirsk, an emergency department physician at the Royal Alexandra Hospital, told CBC News. "It is more patients than any of us want to count right now. It's a disaster. It's a one in every 15- to 25-year disaster."

Acute Care Alberta said several hospitals across the province had activated a "Code Orange," an emergency designation used when multiple severely injured patients require coordinated medical care. The agency said emergency medical resources were stretched so thin that extremely few ambulances were available in the Edmonton area, and it urged people to avoid the University of Alberta Hospital emergency department if possible. The episode underscored how a mass-casualty emergency at a remote training base can strain civilian medical capacity across an entire province.

Wainwright Mayor Bruce Pugh said the town's small hospital was not designed to handle a mass-casualty incident but praised the response of local medical personnel. He said helicopters and planes had been transporting patients to other facilities for treatment.

At least 10 ambulances were parked in and around the Wainwright health center late Saturday as paramedics and soldiers rushed about, and one patient was seen being loaded into an ambulance. The town of Wainwright, near the base, has about 7,000 residents.

Defense Minister David McGuinty said the Royal Canadian Mounted Police were involved in investigating the incident and described the situation as "very, very active and delicate." He said authorities were still working to determine what happened and expected to provide further information.

McGuinty said Sunday he was traveling to Edmonton to be briefed on the latest developments, adding that the military was working closely with Alberta's government and local authorities.

The Canadian Armed Forces had said it would not release casualty figures until relatives were notified. Carney said Sunday that the families of the four service members killed had been informed. The cause of the blaze and a complete accounting of the injured remain the key open questions as the RCMP-led investigation continues.

The RCMP said officers were called shortly after 4 p.m. Saturday following reports of a fire in a training area at the base.

Firefighters faced a volatile situation. Large areas of the province were hit during the day by a windstorm with gusts of up to 100 kph (62 mph), which toppled some trees and sent signs flying and garbage cans rolling down streets. By 11 p.m., the Municipal District of Wainwright said on social media that the fire was being held and that property and critical infrastructure were protected. There was no evacuation order for residents.

Speaking to reporters in Ottawa, McGuinty confirmed the casualties but had no other details to share.

"I cannot recall such an incident in my short time for sure as a minister, but I cannot recall an incident like this in recent memory," McGuinty said.

"We will have more to say in the coming hours and days," he added.

He said Armed Forces members were at the scene and that the RCMP were also involved. "This is an active and delicate situation and soon to be an active and delicate investigation."

Saskatchewan Premier Scott Moe said his province was sending assistance to Alberta but did not specify what resources were being deployed. Alberta Premier Danielle Smith described the fire as "significant and tragic" and said it was affecting many military personnel.

Carney praised the emergency crews who battled the fire through the night and said STARS air ambulance helicopters had flown in from Edmonton and Saskatoon.

CFB Wainwright is one of Canada's busiest military training bases, where soldiers prepare for combat operations. It is home to the Canadian Maneuver Training Center, which conducts realistic battlefield exercises, and the 3rd Canadian Division Training Centre, which provides military training.

Conservative opposition leader Pierre Poilievre said he had spoken with Carney and the defense minister to offer support to those affected by the fire. "Pray for Wainwright, everyone," Poilievre said in a social media post. He urged people in the area to follow emergency instructions and keep roads clear for first responders.

The fire also disrupted advance voting ahead of Monday's referendum on whether Alberta should begin a process that could lead to independence from Canada. Elections Alberta said the advance polling location at Wainwright Communiplex closed early Saturday and that ballots and election materials were transported securely. It identified polling locations in Lloydminster and Vermilion as alternatives.

This story was originally featured on Fortune.com.