The government of Canada's British Columbia declared a state of emergency in the Pacific province on Wednesday due to floods and mudslides caused by rainstorms in the last few days.

British Columbia Premier John Horgan made the declaration at a news conference. "Heavy rains, strong winds, flooding have devastated entire communities of our province."

The declaration gives the province various powers from stopping hoarding to restricting travel in and out of flood zones.

"The order will preserve basic access to services and supplies for communities across the province," Horgan said.

Authorities have confirmed one death after torrential rains and mudslides destroyed roads and left several mountain towns isolated. At least three people are missing. Some 18,000 people are displaced in the Pacific Coast province, Canadian Public Safety Minister Marco Mendicino said.

"Sadly, we expect to confirm more fatalities in the coming days," Horgan said, describing the calamity as a once-in-500-year event.

The premier said he has spoken to Prime Minister Justin Trudeau, adding that his government has now formally requested the assistance of the Canadian Armed Forces.

He said the Trudeau government and provincial governments of Alberta, Saskatchewan and Ontario have offered support to his province.

The floods and mudslides also severed access to the country's largest port in Vancouver, disrupting already strained global supply chains.

The disaster could be one of the most expensive in Canadian history.

The flooding is the second weather-related calamity to hit British Columbia in the past few months. A massive wildfire, in the same region as some of the devastation, destroyed an entire town in late June.

(With input from agencies)