A harmful cloud of smoke darkened the skies from Canada all the way to New York City in recent days.

Air quality dropped to a record low in the metropolis on Thursday, and air traffic had to be rerouted. It will take a long time for the smoke cloud to fully clear.

Smoke from several severe wildfires in Canada has enveloped parts of the east coast of the US.

The pollution levels aren't just extreme for New York – even the most polluted cities in the world rarely see such poor air quality.

The smoke from hundreds of fires in eastern Canada travelled south, causing a dense, foggy haze and sometimes orange skies.

The webcam below shows the sky darkening in just a few hours. Afterwards, there was a burning odour in the air that could be felt in the throat and eyes, causing headaches.

The people of New York were asked to stay indoors if possible, to avoid strenuous physical activity as much as possible and to close their windows.

All outdoor activities were cancelled in schools and kindergartens, and many other outdoor events and some theatre performances were also cancelled. Swimming was cancelled at city beaches and zoos and libraries closed early.

Canada is on fire. Numerous fires have been raging for weeks in Canada's west and now also in the north-east of the country.

The country’s fire departments are unable to control the situation. In the south-eastern province of Nova Scotia, however, the situation has recently eased somewhat.

Forest fires in Canada have become much more frequent in recent years and can be attributed to dry and hot weather that, with global warming, we can expect to see even more of in the future.

Canada is seeing 14 times as many forest fires this year as in the past decade. In the last decade, wildfires have already increased in intensity, so what we're seeing is a dramatic and unprecedented increase.

Not only are forest fires more frequent, they are also spreading faster and becoming more intense… generating more smoke that spreads over larger areas.

As a result, we're now seeing smoke clouds as far as New York.