Americans sweltering under a brutal heat wave are bracing for more.

The National Weather Service issued excessive heat warnings for parts of the eastern and central United States Friday, saying temperatures could soar as high as 39 degrees celsius, with high humidity making it feel like 46.

Already, health officials are blaming the severe heat for at least six deaths. They warned Americans to avoid working outside during the middle of the day and to check on neighbors and relatives.

The National Weather Service is also warning the high temperatures are having an impact on air quality, issuing a so-called “Code Red” alert for the nation's capital, Washington, where temperatures are expected to rise into the 40s.

In New York, the main power company predicted it might break its all-time record for electricity usage as city residents used air conditioners and electric fans to cool down.

New York City residents hoping to cool off by going for a swim got bad news. The city's health department warned residents to avoid two main rivers as well as some area beaches after a fire shut down New York's largest sewage treatment plant, spewing sewage into the waterways.

Meanwhile, it was so hot in Pittsburgh, in the state of Pennsylvania, that a man working on the roof of a house Thursday slipped and got stuck to the tar he was using.

The Pittsburgh Tribune-Review said he was rescued about an hour later.