More than 100 million people under major or extreme heat alerts in the United States

More than 100 million people in the United States were under major or extreme heat alerts Thursday as a heat wave reached its most critical point across the country’s central states.

The National Weather Service said 46.7 million people faced the highest-level, extreme alert. The greatest risk covered parts of the Midwest, including Illinois, Indiana, Missouri and Kansas, while warnings also extended into Texas, Arkansas and North Carolina. Another 71 million people faced major heat alerts across much of the area between Colorado and New York.

The number of people affected is expected to decline toward the weekend, but the National Weather Service warned that dangerous heat could continue in parts of the south-central United States into next week. Heat indexes could reach or exceed 40.5 degrees Celsius across the southern Plains and lower Mississippi Valley, and 43.3 degrees in southern Texas.

Authorities urged people to limit afternoon outdoor activity, drink plenty of water and ensure access to air conditioning or cooling centers. They also advised checking on vulnerable relatives, friends and neighbors, and warned against leaving children or pets unattended in vehicles.

The country has experienced an especially hot summer marked by several heat waves. July was the hottest month in the United States since records began, with an average national temperature of nearly 25 degrees Celsius, according to the National Oceanic and Atmospheric Administration. Heat and drought have also helped fuel wildfires, with more than 3 million hectares burned so far this year, the highest figure in a decade.