The agency warned that extreme heat poses a danger in the evening as well, as temperatures are expected to remain above average overnight. As of Monday morning, nearly 8 million Americans were under heat alerts, according to the National Integrated Heat Health Information System.

Over 30 million people in the US have been under extreme weather alerts since Sunday as a heatwave grips the western part of the country. Excessive heat warnings are in place in parts of California, Oregon,

Red flag warnings now cover parts of Oregon, Washington and California. In Oregon and California, crews are battling flames that are burning thousands of acres. Along the West Coast, heat alerts remain in effect for 11 million people.