WILLIAMS LAKE, B.C. - Ash from wildfires in British Columbia's Cariboo region is falling like snow in Williams Lake, where the Environment Ministry has rated the air quality as the poorest in the province.

Katrina Buckland, who works at the front desk at a downtown hotel, said Thursday that guests, most of them from Alberta and the United States, are complaining about conditions that are causing some to cough and wheeze.

"When you go outside after about nine o'clock when it gets dark here all the ash in the air, you can actually see it falling and we've been making a joke that it's actually snowing in August around here," she said.

Buckland said she's stuffed up and has headaches from the smoke, which the Environment Ministry rated as having a "very high health risk."

"I've had a lot of guests complaining too, about the air quality and the smell. They have the same symptoms. It's just absolutely horrible."

Mornings are the worst for health effects, but nightfall brings falling ash.

Intense, choking smoke from wildfires in the Cariboo is also affecting air quality in Kamloops, B.C., where stores began closing their doors and residents were asked to stay inside.

The Environment Ministry warned children and the elderly should avoid strenuous outdoor activities.

Ralph Adams, an air quality meteorologist with the ministry, said the problem began with a dramatic shift in wind patterns.

"You literally could see the plume of smoke approaching," he said.

The Environment Ministry said smoke concentrations in the Thompson Valley will vary widely, depending on winds, temperatures and forest fire activity.

An Air Canada flight from Vancouver to Kamloops was delayed Thursday morning when it could not land due to poor visibility, said airport operations manager Ed Ratuski.

The airport is asking travellers and those expecting flights to check with its website to determine if flights are delayed.

The smoke also forced the cancellation of six Air Canada Jazz flights from the Kamloops airport.

Forest service planes began checking huge areas of B.C.'s charred woodlands early Thursday morning, trying to determine if erratic overnight winds caused any wildfire flareups.

Fire information officer Gwen Eamer said the northwestern corner of the province took the brunt of a weather system, packing winds of up to 60 kilometres an hour.

She said blazes in the Bulkley-Nechako area of the province, on the inner central coast, grew significantly while 52 active fires in the Cariboo region of the central Interior were not as hard hit.

Shelly Burich, a spokeswoman for the Cariboo Regional District, said more than 2,200 people have been forced out of their homes across the province during the last three weeks.

She said some people have been able to return, but others have had to leave their properties more than once.

Burich said improved conditions on Thursday meant several evacuation alerts and orders were lifted within the regional district.

She said an evacuation alert for residents of 439 homes from the central Chilcotin has been lifted, as was an evacuation order for people from 306 properties in the Anahim Lake area and Heckman Pass.

Forests Minister Pat Bell said most fires in the province grew by only five or 10 per cent overnight, significantly less than originally anticipated.

However, he said a fire at Binta Lake, near Fraser Lake, has grown threefold to about 310 square kilometres, "and we're watching this one very closely."

Chris Duffy, director of operations for Emergency Management B.C., formerly known as the Provincial Emergency Program, said people from 728 properties are currently out of their homes across the province and that a further 1,138 homes are on evacuation alert.