Sizzling high temperatures punished much of the eastern United States again on Saturday, one day after hurricane-like thunderstorms killed at least 11 people and cut power supply to millions.

Thermometers brushed the 100 degree Fahrenheit (37.7 Celsius) mark from the Mississippi River to the Mid-Atlantic coast as a vast area of high pressure squatted over the southern states with no signs of moving on soon.

The storms delayed third-round play at the USPGA Tour's AT&T National in the suburbs of the US capital Washington for several hours, and organizers barred golf fans from attending, creating a surreal atmosphere for the players.

At least 11 people died in storms triggered by the heat wave, CNN reported, and four states -- Maryland, Virginia, West Virginia and Ohio -- declared states of emergency. Some 3.7 million homes in nine states lost power.

President Barack Obama telephoned the four states' governors to express concern for the loss of life and property, and to pledge federal government help, the White House said.

Virginia Governor Bob McDonnell said it would take several days for his state to recover from what he called the biggest non-hurricane-related power outage in its history.

On Saturday, those without power -- and hence without air conditioning -- had no respite from the punishing heat.

"High temperatures this afternoon will exceed 100 degrees across the mid/lower Mississippi River Valley eastward through the Mid-Atlantic and Southeast today," the National Weather Service said.

"In fact, some locations are expected to break record high temperatures," it said, as it issued excessive heat warnings for areas stretching from Illinois to Georgia.

Five of the reported fatalities occurred in and around Washington, where storms packing winds of up to 80 miles (130 kilometers) an hour barreled into the area Friday night.

Two of the dead were elderly women, aged 90 and 71, who were in their beds when trees fell on their respective homes, the Washington Post reported. Another victim died after touching a downed, live electrical wire.

In many communities Saturday, local authorities set up "cooling centers" in schools, libraries and other public buildings to give refuge to those without air conditioning.

Crowds also flocked to relatively cool shopping malls, or lined up at gas stations that still had electricity to power their filling pumps. Screenings at air-conditioned movie theaters sold out.

"If you have air conditioning and have not lost power, consider opening your home to family members or friends who may not have air conditioning and may not tolerate the heat well," Maryland Governor Martin O'Malley said.

Pepco, the electric utility that serves Washington and some of its suburbs, said in an automated telephone message Saturday that 440,000 of its customers were still without power.

"Due to widespread damage, we expect power restoration efforts to take about a week," it said.

At the White Flint shopping mall in Maryland, visitors sat on floors and chairs and plugged their computers and mobile devices into electrical sockets to take advantage of precious free power.

In Bethesda, Maryland, just outside Washington, organizers delayed the start of the third round of the US PGA Tour's AT&T National for six hours at the Congressional Country Club.

"There are trees and tents down all over the course and roads leading to the course. Clean-up has begun. Electricity is out at the course," the PGA said, adding that fans and volunteers would be kept off the course Saturday.

Even social media took a hit, with servers in Virginia that host the popular photography social media site Instagram getting knocked out for several hours, tech blog Mashable reported.