As much as half of a town at the heart of a jewel of Canada’s national park system has been destroyed by a pair of wildfires that roared in from two sides, an official said on Thursday.

“We don’t know particularly which structures have been damaged and which ones have been destroyed, but that is going to be a significant rebuild,” Danielle Smith, the premier of Alberta, told a news conference. She struggled to avoid tears describing the beauty of Jasper National Park and the damage to the community that shares its name.

Pierre Martel, the director of fire management for Parks Canada, the national parks agency, told a briefing on Thursday afternoon that the “aggressive and fast-moving fire” was still burning in the park.

As the fires expanded on Monday evening, about 20,000 tourists and the 5,000 residents of Jasper were evacuated, mostly west to British Columbia.

On Wednesday night, wildfire fighters had to leave the town because of toxic smoke from the buildings that had caught fire. Parks Canada, which is in charge of fighting the fire, also moved its command post.

Fire fighters from other communities have since arrived to help fight the blaze, which follows a recent heat wave.