(CNN) -- Widespread power outages struck Venezuela on Tuesday afternoon at an hour of peak demand, an official said.
"It's affecting quite a few areas of the country," Luis Diaz Curvelo, national director of civil protection, told Globovision Television. It said that about 40 percent of the country had been blacked out since about 4:15 p.m. local time (4:45 p.m. ET).
The president of the Electric National Corporation, Hipolito Izquierdo, told state-run Venezuelan Television that power would begin returning by 5:30 p.m. (6 p.m. ET).
He said most of the eastern part of the country was unaffected.
"We're taking all action to ensure this does not recur," he said, adding that such blackouts usually are the result of a convergence of factors. In this case, he cited high temperatures as a contributing factor.
Hospitals were using emergency power.
Affected zones included parts of the capital city of Caracas -- where streetlights were dark -- and the states of Zulia, Lara, Carbobo, Yaracuy, Portuguesa, Miranda, Falcon, Merida, Aragua, Bolivar and Tachira, the station said.
Gustavo Gonzalez, president of Caracas Metro, the city's rapid-transit system, said it was functioning normally. But a ticket seller at one station said train service had been halted and riders were being diverted to buses.
"Normally, these blackouts don't occur very often," said Javier Alvarado, president of Caracas Electricity. [link to www.cnn.com]