The rapid growth of an out-of-control wildfire has prompted evacuations in British Columbia's Thompson-Nicola region as the number of fires spike and the wildfire service braces for what's expected to be a "very challenging" 72 hours.

Emergency Management Minister Bowinn Ma said the Shetland Creek fire grew "quickly and considerably" Wednesday night to span nearly 50 square kilometres, and residents had no notice ahead of the "tactical evacuations" overnight.

Ma was in Kamloops, where she told a news briefing that the situation is "very dynamic" and she couldn't yet confirm the specific number of evacuees.

The evacuation order from the Thompson-Nicola Regional District covers 76 properties in the Venables Valley area north of Spences Bridge.

The director of provincial operations for the BC Wildfire Service joined Ma, telling the briefing that the Shetland Creek fire had displayed "aggressive" behaviour Wednesday night, challenging their suppression efforts.

Cliff Chapman said the service deployed its night-vision-equipped aircraft to a fire for the first time this year, flying over from Penticton to help the groundcrews.

An incident management team was getting set up in the area Thursday, he said.

A blaze discovered Thursday on the east side of Slocan Lake in southeastern B.C. also prompted the Regional District of Central Kootenay to issue an evacuation order. It covers 11 properties along Highway 6 south of the community of New Denver.

The fires are among at least 220 active across B.C., a significant jump from fewer than 180 on Wednesday. Just over half are classified as burning out of control.

Chapman said he believes the province is "on the precipice of a very challenging 72 hours" with hot, dry weather, dry lightning and strong winds in the forecast.

"For all of British Columbians, my message is (to) be diligent. We are going to see lightning. We saw 1,300 lightning strikes (Wednesday), many of which started fires in the southeast fire centre, and we'll pick up more (on Thursday)," he said.

The wildfire service is focused on aggressively attacking fires as quickly as possible, but conditions are ripe for new starts and rapid growth, Chapman said.

He told the news briefing that he hadn't heard of any structure damage due to the fire near Spences Bridge, although it was "threatening" structures.

The evacuation order from the regional district said residents were to report to the emergency services reception centre at the community hall in nearby Cache Creek.

Cook's Ferry Indian Band has also expanded an evacuation order related to the same fire to include additional reserves along the Thompson River.

The fire was discovered last Friday and then merged with the smaller Teit Creek fire. Lightning is the suspected cause.

The forecast for Cache Creek, north of the Shetland Creek wildfire, shows a daily high of 40 C on Thursday, 38 C on Friday and 40 C over the weekend.

Environment Canada has issued more than two dozen heat warnings throughout B.C., covering Howe Sound and Whistler, the Fraser Canyon, parts of the Thompson, Okanagan and Kootenay regions, inland sections of the north and central coasts, the northeast corner of the province along with much of the central Interior.

A bulletin from the wildfire service Thursday said the hot, dry conditions mean the landscape is primed for new fire starts.

– By Brenna Owen in Vancouver