Bushfires in Canada have caused a deterioration in air quality on the east coast of the United States, where smoke effects on Wednesday reached and spread widely.

The Swiss website "IQ Air" - specialized in monitoring the state of the air - revealed that more than 55 million people are exposed to air pollution in the northeastern and central United States, due to wildfire smoke coming from Canada.

The site said that the fires affected air quality significantly in several cities, most notably New York and Boston, where air pollution reached dangerous degrees, leading to discoloration of the sky and poor visibility.

An orange cloud of smog overshadowed skyscrapers and forced residents to wear masks.

Meanwhile, officials warned of health risks and advised wearing masks in areas most vulnerable to contamination.

Authorities advised New Yorkers to wear masks due to heavy smoke from Canada (Reuters)

The US Environmental Protection Agency announced in a statement that more than 100 million citizens are covered by warnings related to the deterioration of air quality due to fires in Canada.

The warnings cover much of the northeastern United States from Chicago in the north to Atlanta in the south.

According to a report by the U.S. National Weather Service, air quality in Washington, D.C., has dropped to dangerous levels.

Very poor air quality was recorded for people with heart and lung disease, as well as the elderly, children and adolescents.

Thirteen U.S. states have issued alerts for smoke and fumes blocking their views and have ordered people to stay indoors since Wednesday morning.

For its part, the White House yesterday called on Americans with health problems to take appropriate precautions to prevent air pollution on the East Coast from wildfires sweeping Canada.

New York's famous Statue of Liberty appears faded due to heavy smog (Reuters)

White House spokeswoman Karine Jean-Pierre said: "We encourage everyone in affected areas to be alert to local conditions. Make sure your neighbours, friends and family are well," she said, adding that the situation is "a worrying example of the ways climate change is affecting our lives."

Plumes of smoke from Canada's unprecedented bushfires also limited the impact on flights in the New York area yesterday.

The Federal Aviation Administration briefly suspended some flights to LaGuardia and Newark Liberty International Airports. It said it had taken steps to manage traffic to the New York area because of reduced visibility as a result of smoke from the fires.

Clouds of smoke from Canada cover the White House in Washington, D.C. (Reuters)

Canadian authorities said they were trying to put out about 400 fires, more than half of which were out of control.

Canadian officials said firefighters were working to put out the fires in the province of Quebec, where more than 160 wildfires are currently active.

Evacuations continue in the province of Quebec, which has become the epicenter of wildfires ravaging much of Canada.

Public schools in the provinces, which have been affected by the smoke from Canada's bushfires, have cancelled outdoor activities, including sports.