Weather forecasters say a record heat wave baking the eastern United States will continue at least through this week.
The heat is especially hard on more than 2 million people who remain without power in the region, following severe storms late Friday that toppled trees and cut off energy supplies.
At least 20 deaths have been blamed so far on those storms and the extreme heat that has followed, and there are concerns that others, especially the sick and elderly, may be at risk.
Power outages have persisted from the East Coast as far west as the state of Illinois.
With temperatures hovering around 40 degrees (Celsius) many homes have no functioning air conditioning or refrigerators. Utility companies warn that it could take all week to restore electricity to some locations.
Power crews from other states have been called in to help get power restored.
The nation's capital, Washington, and some states, including Maryland, Ohio, Virginia and West Virginia, have declared states of emergency.
Officials are urging residents to check up on elderly or sick neighbors and to seek cool shelters if their homes have no power.
Washington resident Pat Armelin said the entire block in northwest Washington where she lives has been without power since the storm hit. She expressed concern about her 92-year-old neighbor who was trapped in her home after a large tree fell on cars blocking access to her house.
"I have a next door neighbor who is 92-years-old and cannot get out of her house," said Armelin. "The tree here has landed on both of their cars, and if it was an emergency the firemen would be the only ones who could go in and be able to get her. And with no air conditioning and the heat in the 90s, it has been very frustrating."
Some secondary roads remain closed to traffic because of fallen trees awaiting removal.
Extremely hot temperatures in the U.S. Midwest have stressed crops in their critical stage of development, raising concerns about crop failures.