At least 37 people have died in a severe heat wave that has been spreading eastwards across the US.
At least 20 people died in Phoenix, Arizona
Heat warnings were issued in nine eastern states and in the cities of Philadelphia, Washington and Baltimore.
High temperatures boosted power demand to record levels as people sought refuge in air-conditioned buildings.
And around 300 boys were taken ill at the Scout Jamboree in the state of Virginia, hours before President George W Bush was due to visit.
Mr Bush was scheduled to attend a memorial service on Wednesday for four scout leaders who were electrocuted earlier this week after pitching their tent underneath a power line. He later postponed the visit for a day.
Temperatures topped 38C (100F), hitting record highs in Florence, South Carolina and Raleigh-Durham in North Carolina on Tuesday.
DEATHS FROM THE HEAT
Arizona - at least 28
Missouri - 4
Oklahoma - 2
Kentucky - 1
Ohio - 1
Mississippi - 1
New York City power usage reached a new record of 12,551 megawatts, as Mayor Michael Bloomberg announced the opening of special public air-conditioned "cooling centres".
Most of the deaths came in the south-western state of Arizona.
At least 20 people died in the city of Phoenix, most of them homeless.
And there were reports that 21 immigrants had died while trying to cross to the US from Mexico.
At least 1,200 cattle died as a result of the heat in Nebraska.
A cold front brought relief but also severe thunderstorms for the mid-West by Wednesday.
However, forecasters were predicting another scorching day on Thursday for the country's south-east.