A water tanker drops a load of fire retardant on the Blackcomb fire Thursday afternoon. (CBC)

Nearly 3,000 residents have been alerted to be ready to leave their Lillooet, B.C., homes at a moment's notice as the premier warned the province's wildfire risk has reach a critical level heading into the long weekend.

The eastern flank of the Mount McLean suddenly roared to life on Thursday evening, and provincial fire information officer Kim Steinbart said firefighters are working hard to extinguish the 21-square-kilometre wildfire, which is burning uncontained about four kilometres from the southwestern Interior town.

An evacuation order is already in place for properties on the northeast shore of Seton Lake, an area east of the Silicon Indian Reserve 2, and Puck Creek. The new evacuation alert now applies to Lillooet, Shalalth, Seton Portage, and the First Nations community of T'it'qet.

The Mount McLean fire is one of 531 burning across B.C. during a record-setting heat wave this week. On Thursday alone, 171 fires were started across B.C., primarily from lightning.

On Friday morning, Premier Gordon Campbell asked the public to voluntarily avoid travelling in remote backcountry areas to reduce the risk of accidentally starting a fire or getting caught by a wildfire themselves.

"With high temperatures and lightning expected as we head into the B.C. Day long weekend, every British Columbian needs to take an active role in ensuring the safety of their community by being vigilant and cautious," Campbell said in a statement released Friday morning.

Backcountry restrictions under consideration

Human-caused wildfires are totally unpredictable and dangerous to firefighters, and the province is considering restricting backcountry travel if conditions become worse, Campbell said.

B.C. Premier Gordon Campbell points to maps showing 85 per cent of B.C. is at a high or extreme fire hazard risk. (CBC)

There is currently a ban on campfires and open burning across B.C., and those who fail to comply with burning restrictions could face a $345 fine. Many municipal parks have also banned smoking and open-flame barbecues.

"The wildfire risk is at the highest level in recent memory, with 85 per cent of the province facing a high or extreme fire hazard level," the premier said.

All six provincial fire centres are on high alert with fire hazard ratings in the high or extreme range now covering more regions of the province than in 2003, when forest fires in the Okanagan Valley destroyed 239 homes. Severe thunderstorm warnings are in place for many areas of the province as well.

Since April 1, the firefighters have battled a staggering 1,817 wildfires that have burned approximately 51,042 hectares of forests and grasslands. About half of those fires were human-caused, according to figures released by the province on Friday. By comparison, at this point in the 2003 there had been 959 fires and 31,000 hectares burned in total.

Lightning strikes spark blazes across B.C.

On Thursday a fire in Tweedsmuir Provincial Park closed Highway 20, the only road between the coastal communities of Bella Coola and Anahim Lake on the Central Coast. That fire started with a lightning strike and quickly grew to 30 hectares by nightfall.

In the northwestern Interior of the province, the Kispiox fire grew to 80 hectares, and although residents in the area could see smoke, no structures were in danger, said officials.

In the far north, a lightning strike caused a fire that is keeping crews busy north of Fort St. John, and in the Cariboo region, a fire near Kersley was in the mop-up stage as of Friday morning.

A wildfire east of Quesnel, in the central Interior about 70 kilometres from the community of Likely, remains at 150 hectares.

A large fire is also burning on Blackcomb Mountain, north of Vancouver at the Whistler ski resort, but that fire is not threatening any homes or structures, and the Whistler portion of the resort and businesses in the village are expected to be open on Friday.

On the northwest shore of Okanagan Lake the Terrace Mountain fire is still about 85 per cent contained, and most residents were allowed to return to their homes on Thursday.