An avalanche struck an informal snowmobile rally in Canada's Rocky Mountains, killing at least two people and leaving an unknown number missing at an annual gathering best known for its party atmosphere and stunt riding.

Rescuers sent helicopters over remote Boulder Mountain at daybreak Sunday to determine if conditions were safe for a full-scale ground search after operations were halted overnight when darkness fell.

Police also conducted a door-to-door search of hotel rooms Sunday to piece together how many people were missing from the Big Iron Shoot Out rally that drew about 200 people to the mountain.

Revelstoke Mayor David Raven said an avalanche warning had been in place for three weeks.

"A fresh snowfall overnight exacerbated that warning. I know people have been cautioned again and again," Raven told CTV Newsnet.

Royal Canadian Mounted Police Cpl. Dan Moskaluk told a news conference Sunday morning that two people are confirmed dead in the avalanche, not three as previously reported in the chaotic hours after the slide.

Moskaluk said 30 people were injured, including one person in critical condition and three others in serious condition. He said 19 people were treated and released at the local hospital.

About 200 people were on the mountain when the slide struck around 3:30 p.m. local time Saturday, but many of them survived and got off the mountain safely. The Big Iron Shoot Out is an annual unsanctioned but increasingly popular informal gathering of people who enjoy snowmobiling in the deep snow of backcountry British Columbia.

Moskaluk said there could be some people still buried on the mountain, but it is not known how many.

"I don't think we want to ever give up hope. Certainly there is faint hope at this time. However, being realistic we are referring to this as a recovery/rescue operation," he said.

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

She said the slide occurred in a place called Turbo Bowl, at the foot of the mountain, and a group of people, including parents with children, had gathered to watch the snowmobiles go up the hill when the avalanche broke through.

"One fellow that I was talking to said that it resembled a war zone," Berlingette said.

Berlingette said she had five guests who came to town for the rally, and all survived the avalanche.

One survivor who came from Fort St. John, in northern British Columbia, for the rally described a "big white wall of snow" coming down on his group of about 20 to 30 snowmobilers.

The man, who did not want to give his name, said they saw the slide coming and had only a few seconds to react. He dove behind his snowmobile, and ended up partially buried. Members of his group dug him out.

The avalanche occurred near Revelstoke, about 300 kilometers (185 miles) west of Calgary and about 400 kilometers (250 miles) northeast of Vancouver.

Search and rescue teams, including helicopters and avalanche-trained dogs, were called in from around British Columbia and Calgary, said RCMP Cpl. Dan Moskaluk.

Ervin McKeen, 62, was nearby when the snow came down and tossed snowmobiles around everywhere. He said one man was screaming "Where's my son?" as he desperately searched the area.

McKeen, an experienced backcountry user, said he used his equipment to lead survivors with shovels to places in the snow where electronic avalanche beacon signals indicated people might be buried.

The Canadian Avalanche Center had issued a warning for the region for Saturday and Sunday, after a powerful storm blanketed the area with snow.

Greg Johnson, from the avalanche center, said at the time that there was danger that the snow would overload weak layers in the upper snowpack.

Adam Burke, 20, a member of the Revelstoke Snowmobile Club, said his mother and many of his friends were up on the mountain when the avalanche struck. His mother was safe, but at least one family friend was unaccounted for.

Burke said he chose not to go to the rally because of the dangerous conditions in the mountains this weekend.

"I told everyone to shut the mountain down. ... I told my mom ... don't have anything to do with this event."

Burke said the Big Mountain Shoot Out was started by a Calgary businessman several years ago, and got bigger over the years. It has a reputation for having a party atmosphere, with many riders and onlookers gathering to watch riders perform stunts, such as high-marking, where snowmobilers compete to see who can ride their high-powered sleds the highest up a steep slope.

There have been a few avalanche deaths in the British Columbia backcountry this season but nothing compared to last winter, when there were two dozen deaths. There were 13 avalanche deaths the previous winter.