Americans dipped into the water, went to the movies and rode the subway just to be in air conditioning Saturday for relief from unrelenting heat that has killed at least 30 people across half the country.

The heat sent temperatures soaring over 38 degrees Celsius in several cities, including records in Washington (40.5 C), St. Louis (41 C) and Indianapolis (40 C), buckled highways and derailed a Washington-area train even as another round of summer storms threatened.

More than 20 states experienced temperatures in the mid-30s Celsius and higher, from Kentucky to Maryland to South Dakota.

At least 30 deaths were blamed on the heat, including nine in Maryland and 10 in Chicago, mostly among the elderly. Three elderly people found dead in their houses in Ohio had heart disease, but died of high temperatures in homes lacking power because of recent outages, officials said.

Heat was also cited as a factor in three deaths in Wisconsin, two in Tennessee and three in Pennsylvania.

Officials said the heat caused highways to buckle in Illinois and Wisconsin. In Maryland, investigators said heat likely caused rails to kink and led a train to partially derail in Prince George's County on Friday afternoon. No one was injured, and 55 passengers were safely evacuated.

Electricity still out

Thousands of mid-Atlantic residents remained without power more than a week after deadly summer storms and extreme heat struck the area, including 120,000 in West Virginia and some 8,000 in the suburbs around Baltimore and Washington, D.C. In the Washington area, the utility company Pepco asked customers to conserve power, saying the heat was stressing the system.

In Manhattan, where temperatures climbed to 35 degrees C, customers who stepped in to see Jiro Dreams of Sushi at a repertory movie theatre were there for more than entertainment.

"Of course we came to cool off!" said John Villanova, a writer who was on his second sweaty T-shirt of the day — expecting to change again by evening.

He said that earlier, he rode a Manhattan subway back and forth for a half an hour, with no destination in mind, "because it really keeps you cool."

In cities around the Midwest and Mid-Atlantic region, people struggled to find ways to cope with the heat, but at least one such effort ended in tragedy.

In Aurora, Ill., Gene Autry Pryor, 52, had been drinking with three adult friends near Veterans Memorial Island and jumped into the Fox River to cool off, police said. The man's friends lost sight of him after a few minutes and then spotted him floating face down and pulled him to shore. Pryor died Friday evening.