NEWYORK-High temperatures with high humidity currently gripping a large swath of the United States across the Midwest, South and the East Coast is expected to continue through Sunday, July 21.

The heatwave could affect about 200 million people in major cities like New York, Washington and Boston in the East Coast, and the Midwest region too, according to weather experts.

In some places, temperatures could be close to or exceed 100F (38C). Parts of Canada are also being hit.

Experts link more frequent heat waves in recent years to climate change. The world experienced its hottest June on record this year, with an average temperature worldwide of 61.6F (16.4C), according to new data.

Earlier this month, the US state of Alaska, part of which lies inside the Arctic Circle, registered record high temperatures.

The heat wave is hitting an area stretching from the Central Plains of Colorado and Kansas, to the Great Lakes in the north-east.

Temperatures are also rising in most areas of the East Coast. The National Weather Service (NWS) published a map of the areas that are affected.

“The hazy, hot and humid conditions will persist through the weekend. Be smart and stay cool!” it warned.

New York Mayor Bill de Blasio declared “a local emergency due to the extreme heat” in the city.

“This is a heatwave coming up these next days. Its serious stuff,” the mayor said in a video posted on Twitter. “Saturday is going to be really, really bad on through Sunday.”