Smoke alerts as Canada fire spreads

Fort McMurray Fire Captain Adam Bugden: "I've met more heroes in this experience than I ever thought existed"

Air quality warnings have been issued for Saskatchewan and Northwest Territories in Canada as a huge wildfire continues to spread.

Locals have been advised to close windows and doors due to smoke.

Now in its seventh day, the blaze has doubled in size, fuelled by hot weather and tinder-dry terrain.

It covers an area of more than 700 sq miles (2,000 sq km) and officials say only significant rainfall will be able to bring it under control.

One report said the blaze had already spilled from the province of Alberta into neighbouring Saskatchewan but this has not been confirmed.

Two fires have been approaching the border, the closest about 22 km (13 miles) away, officials told CBC.

Chad Morrison of the Alberta Wildfire authority said it was moving away from communities and some rain was due Sunday.

The blaze prompted the mass evacuation of 80,000 people from the oil city of Fort McMurray, most of whom fled south.

About 25,000 headed north after the mandatory order to leave was issued.

Most have since been escorted south by road or air and the Premier of Alberta, Rachel Notley, said she hoped to complete evacuations by the end of the Sunday.

The fire is expected to be the most expensive natural disaster in Canadian history, with insurance costs alone already running into billions of dollars.

The blaze ruined entire neighbourhoods in Fort McMurray, with residents warned it could be some time before they can return.

Officials say the power grid is damaged and the water undrinkable.

Some 1,600 homes and other buildings have been lost but no deaths or injuries have been reported.

Air quality warnings have been issued

The blaze has devastated whole neighbourhoods in Fort McMurray

The blaze doubled in size in the space of a day and is spreading further

In the rush to leave, some Fort McMurray residents were forced to flee without their pets and a website has been set up so volunteers can reach stranded animals.

"We're hearing about lots of dogs and cats, but also one guy has 32 geckos that need rescue," Shannon Orell-Bast told the Globe and Mail.

More than 500 firefighters are battling the blaze with helicopters, air tankers and other heavy equipment.

Nick Waddington from the Fort McMurray Fire Department said one crew member saw his house burn down before going on to work an 18-hour shift.

Fort McMurray is in the heart of Canada's oil sands country, and the region has the world's third-largest reserves of oil.

As much as a quarter of the country's oil production has been halted by the fire, raising concerns about the effect on the Canadian economy.

There are warnings the blaze could burn to the edge of a facility run by Suncor Energy but officials said the risk of damage was low.