Firefighters in Canada are fighting to contain several forest fires that have destroyed large swathes of land in the eastern province of Quebec.

The fires, thought to have been caused by lightning strikes, have sent clouds of smoke over the country's border with the United States as far as Boston and Washington DC.

Up to 500 firefighters have been dropping water from planes over a group of 45 fires in the Lake St Jean region around 240 kilometres (150 miles) north of Quebec City.

However they are being hampered by a lack of rain - none has been forecast until Thursday - and a tendency for the water to evaporate before it hits the fires.

"These are really big fires, we are using firebreaks, sprinklers, hoses and motorized pumps," spokesman for the Quebec Forest Service Eric Santerre told the Associated Press news agency.

"We need rain to bring down the amount of smoke before we can go in."

Safety fears

A further 75 firefighters have dug firebreaks and poured water on a second group of about 40 fires in the Nemiscau region south of James Bay, where around 630 people were evacuated from villages because of safety fears.

Smoke has blanketed the city of Montreal, leading city officials to warn children, the elderly and people with respiratory problems to remain indoors due to health fears.

The US states of New York, New Jersey and Pennsylvania also advised residents with respiratory and heart conditions to stay indoors, with New York and New Jersey's warnings extending state-wide, Pennsylvania's extending to 20 counties.

Since the fires began last week up to 100,000 hectares (250,000 acres) of land have been destroyed, officials from Quebec's forest fire protection service said.