New York has for the last two days been covered in a thick orange-tinged haze as smoke from wildfires burning in the Pacific Northwest swept 3,000 miles across the US to blanket the East Coast.

Massive infernos which have been burning for more than two weeks in parts of Oregon, California and southern Canada spewed smoke and ash up to six miles high, which has now reached the opposite side of the continent.

“Due to the fact that smoke particles are small and light, they can be transported hundreds if not a few thousand miles away from their source,” said AccuWeather Meteorologist Alex DaSilva.

Residents of New York, Boston, Washington DC and Philadeliphia awoke on Tuesday and Wednesday to a red sun and extremely poor visibility.

How wildfire smoke is spreading across the United States

In New York City, where a gray smog shrouded Manhattan’s skyline, the air quality index (AQI) for fine particulate matter reached 170, a level considered harmful even for healthy individuals and nine times above exposure recommendations of the World Health Organisation. Officials urged people not to go outside unless it was necessary.

The US Department of Environmental Conservation noted that while it was not rare for traveling wildfire smoke to reach the New York region, the smoke usually stayed high in the atmosphere. In this case, “data showed that the smoke is extending down to the ground level,” since much of it is coming from relatively nearby fires in western Ontario.

Statue of Liberty seen through cover of wildfire smoke in New York City

Manhattan seen through cover of wildfire smoke in New York City

"We’re seeing lots of fires producing a tremendous amount of smoke,” said David Lawrence, a meteorologist with the National Weather Service. “By the time that smoke gets to the eastern portion of the country where it’s usually thinned out, there’s just so much smoke in the atmosphere from all these fires that it’s still pretty thick.

"Over the last two years we’ve seen this phenomenon."

Climate change is making wildfires larger and more intense, with results visible from satellites and on the ground. The Bootleg Fire in Oregon now covers more than 388,000 acres and is so intense that it is essentially making its own weather. 

As of Wednesday, an army of some 2,200 personnel had managed to carve containment lines around 30 per cent of the fire’s periphery, while the blaze expanded farther to the east and north.

Incident commander Rob Allen said in his daily report that tinder-dry fuels within the fire zone would "continue to burn and produce smoke for weeks."