Four members of the Canadian military have died and dozens were injured in a major fire at a base in the province of Alberta.

Addressing the nation on Sunday from Ottawa, Prime Minister Mark Carney described it as “one of the worst tragedies for the forces on Canadian soil in peacetime”.

The fire broke out at about 16:00 local time (22:00 GMT) on Saturday at Canadian Forces Base Wainwright, one of the country’s busiest military training bases, and is now contained. Its cause is still unclear, but officials said it did not appear tied to “terrorist activity”.

“The nation is in mourning for those brave members of our armed forces who we have lost,” said Carney.

The BBC has confirmed that Sgt Morgan Wong, Pte Shaun Farrell, Pte Aidan Goulding and Pte Hayden Lykkemark have died.

Of the 39 injured people being cared for in hospital, at least 19 are in a critical condition, Alberta Premier Danielle Smith said at a press briefing on Sunday evening.

Fire and rescue teams are remaining at the scene to contain any potential flare-ups, Wainwright Mayor Bruce Pugh told the BBC.

Members of the infantry had been conducting “high-intensity combat training with live munitions” at a grenade range and attack range, where 10 soldiers practise attacking a simulated enemy, Maj-Gen Wade Rutland told reporters at the briefing.

“There was a multitude of ordnance moving through the Wainwright training area,” he said, including a grenade launcher, grenades, small arms and ammunition.

A grass fire ignited about 1km (0.6 miles) away, with the cause currently under investigation, and moved toward the attack range.

“What I would say is there was multiple training activities happening throughout the training area at the time,” he said. “Uncommonly strong winds caused the fire to spread rapidly and shift direction towards the range administrative area.”

Cannon fire had been heard coming from the base on Saturday before it suddenly stopped, Mayor Pugh told the BBC, noting it’s not uncommon to hear cannons being fired there.

News then came through that local emergency services had been deployed to an “all hands on deck” situation.

Carney said military and emergency crews fought the flames throughout the night in “some of the worst conditions imaginable”.

The people who were hurt were on the attack range and included reservists and soldiers from the Princess Patricia’s Canadian Light Infantry, officials said.

In a statement early on Sunday, the Canadian Armed Forces said that “while the incident remains under investigation, at this time, there are no indications that it was the result of any terrorist activity”.

Rutland told the briefing: “We do not believe this [incident] to be a result of any oil and gas infrastructure nor any outside interference”.

Wainwright, about 210km (130 miles) east of Edmonton, Alberta’s capital, is one of the main bases used by the Canadian military for live-fire training exercises, and it houses troops from Canada and allied countries. About 690 military personnel and 300 civilian workers are on site on a typical day.

Warren Thirsk, an emergency department doctor at the Royal Alexandra Hospital, told broadcaster CBC that the number of patients involved in the incident had “completely overwhelmed” healthcare facilities in Wainwright.

The Royal Alexandra Hospital is in Edmonton, where patients are being transferred. The hospital at first declared a code orange – a disaster-response protocol for a high-casualty incident. That has since been stood down.

The provincial health agency said in a statement on Sunday that it deployed 30 units directly into Wainwright, including 22 ground ambulances, six fixed-wing and two rotary wing units.

“It is anticipated that care for patients impacted by this incident will be intensive and will add to existing high demand on acute care in Alberta,” it said, adding that patients were being treated at facilities across the province.

STARS, the regional air ambulance service, said aircraft and crews from Edmonton, Saskatoon, and Calgary had been deployed.

Brandon Simmons, who lives in long-term care at the Wainwright Health Centre, told Reuters that when code orange was announced, nurses dropped everything and immediately started grabbing stretchers, gurneys and medical equipment before running to the front entrance.

Ambulances kept coming “throughout the night”, he said.

“I heard people screaming inside of those vehicles that will never end up being out of my mind,” he recalled, saying it was “like a scene from a war movie”.

Additional reporting by Lisa Lambert