Three people are confirmed dead and two others are in critical condition after an avalanche struck an annual snowmobiling event in southeastern British Columbia on Saturday.

Seven more people are listed in serious condition at hospital, Chris Harbord of the BC Ambulance Service told CBC News.

It is not clear whether more people may be missing. Rescuers were still scouring remote Boulder Mountain, near Revelstoke, early Sunday morning, the RCMP said.

Hundreds of people watching and participating in the Big Iron Shootout, an annual snowmobiling event, were caught in the slide.

Reports indicate the avalanche struck at about 3 p.m. local time.

"The area has been shut down to keep people out," said Cpl. Dan Moskaluk. "They're going to continue on here with trying to remove people off the mountain in the area and tomorrow reassess where we're at."

The mountain was shut down as search-and-rescue helicopters and avalanche dogs worked to recover the injured.

"I know that the RCMP are up there with a number of their members doing searches and that they've got dog units … and the local search and rescue group," Revelstoke Mayor David Raven said shortly after the tragedy occurred. "We also have the ski patrol from Revelstoke Mountain Resorts available and going up."

He said the provincial government has already reached out to offer its support.

"I have been contacted by Kash Heed, the solicitor general, and the province is fully behind all of our efforts and we appreciate all of the help we have now, and it's another trying event for Revelstoke."

Event 'a problem for years'

Raven said he wasn't sure how many people were in the area at the time of the slide, but he did say the Big Iron Shootout is an unsanctioned event "that's been a problem for years."

Kathy Berlingette, owner of Smokey Bear Campground Resort in the area, said the event was in a remote place and everyone involved had to use their snowmobiles to get there.

She said the slide actually occurred on Turbo Mountain, beside Boulder Mountain, and said witnesses told her there were three dead. RCMP were able to confirm only one fatality.

"The audience was below this large mountain. There's a whole group of people watching the snowmobiles go up the hill and an avalanche broke through," said Berlingette, who wasn't there but had guests who took part.

According to the Canadian Avalanche Centre, there have been 10 avalanches in the area since Friday, when the CAC issued an extreme avalanche warning for the area. It advised people to stay away from any defined avalanche terrain and steep slopes.

On Feb. 15, an Alberta man was killed in an avalanche while snowmobiling on Eagle Mountain near Revelstoke. Another Alberta man died in an avalanche while skiing near Rossland, B.C., in early January.

Revelstoke is approximately 300 kilometres west of Calgary, and about 400 kilometres northeast of Vancouver.

With files from The Canadian Press