Temperatures soared to more than 38 degrees Celcius in several cities as Americans dipped into the water, went to the movies and rode the subway just to be in air conditioning for relief from unrelenting heat that has killed at least 30 people across half the country, - AP reported.

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

Temperatures soared in more than 20 states to 40.5 C in Louisville, Kentucky, 38.5 C in Philadelphia, and 35 C in New York; besides Washington, a record of 40 C was set in Sioux Falls, South Dakota, and Baltimore set a record at 39 C.

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.