Canada fires: B.C. under state of emergency, wildfires close main highway

KELOWNA, British Columbia, Aug 19 (Reuters) - Thousands of British Columbia (B.C.) residents were on high evacuation alert on Saturday after rapidly intensifying wildfires forced the Canadian province to declare a state of emergency, while some sections of a key transit route between the Pacific coast and the rest of western Canada were partially closed.

The western province of B.C. has experienced strong winds and dry lightning in the past 36 hours due to a cold mass of air interacting with hot air built-up in the sultry summer. That intensified existing forest fires and ignited new ones.

By Friday, an out-of-control fire in southern B.C. grew more than one hundredfold in 24 hours and forced more than 2,400 properties to be evacuated. The fire was centred around Kelowna, a city some 300 kilometres (180 miles) east of Vancouver, with a population of about 150,000.

As conditions continued to deteriorate quickly through Friday evening, Premier Daniel Eby declared a province-wide state of emergency to access temporary authoritative powers to tackle fire-related risks.

"This is an historic wildfire season for British Columbia," Eby told a briefing.

The fires moved so rapidly on Friday that the number of people under evacuation order went from 4,500 to 15,000 in an hour, while another 20,000 were under evacuation alert. The province currently accounts for over a third of Canada's 1,062 active fires.

"The state of emergency declaration ... communicates to people across the province the seriousness of the deteriorating situation," Eby said. "(It) enables a number of legal tools for us to issue specific orders and to ensure that resources are available."

The flames have already destroyed several structures in West Kelowna and authorities have been warning that the province could potentially face the worst couple of days of the fire season this year.

The TransCanada highway was closed near Chase, around 400 km northeast of Vancouver, and between Hope, 150 km east of Vancouver, and the village of Lytton. However, the government's Drive B.C. said detours were available.

TransCanada is the main east-west artery used by thousands of motorists and road freight heading to Port of Vancouver, the country's busiest.

Some 5,000 customers are also without electricity in interior B.C. due to the fires, the main utility said.

Forest fires are not uncommon in Canada, but the spread of blazes and disruption underscore the severity of its worst wildfire season yet.

The fires have drained local resources and drawn in federal government assistance as well as support from 13 countries. At least four firefighters have died in the line of duty.

About 140,000 square km (54,054 square miles) of land, roughly the size of New York state, have already burnt, and government officials project the fire season could stretch into autumn due to widespread drought-like conditions in Canada.

The escalation in B.C. comes as the northern Canadian city of Yellowknife evacuated most of its roughly 20,000 residents due to a large approaching blaze.

People left their homes and property behind on Thursday and Friday to seek refuge in neighbouring provinces due to the threat of the creeping fire cutting off land exits and potentially doing worse harm.

Residents and tourists drove away on roads flanked by fire and smoke, while local and federal authorities flew out some others.

The massive blaze threatening Yellowknife, the Northwest Territories' capital city, made little headway on Friday as firefighters held it back.

But strong winds could still blow the blaze toward the city, and it could reach the outskirts this weekend, the territory's fire service has cautioned.