( CNN ) -- Power returned slowly to Venezuela on Tuesday night , a few hours after widespread outages blacked out nearly half the country , trapping people in elevators , stalling subways , filling streets with pedestrians and forcing hospitals to switch to emergency generators . The streets of Caracas , Venezuela , are thronged with people during Tuesday 's power outage . `` We understand that at 1600 hours -- that is to say at 4 p.m. ( 4:30 p.m . ET ) -- there was a blackout on a national level that was produced by an explosion , which is being investigated '' in the Guri hydroelectric power station , Caracas Mayor Juan Barreto said . `` That produced a blackout in 16 states of the country , particularly those of the central north coastal area . '' The city 's emergency plan kicked in , and about 400 firefighters in training had reported for duty to help , he said . City firefighters had gone to 37 buildings in the capital to free people from elevators . The head of the country 's electric authority , Hipolito Izquierdo , told state-run Venezuelan Television that 60 percent of the power had been restored by 7 p.m. local time ( 7:30 p.m . ET ) and predicted that power would be fully restored before 9:30 p.m. ( 10 p.m . ET ) . `` We are now recovering , '' he said . Minister of Interior and Justice Ramon Rodriguez Chacin blamed a fault in a generator at the plant in Guri , which caused a high-voltage power transmission line to overheat . In taking the line out of service , power was disrupted to other areas , he said . In all , about 40 percent of the country was blacked out , officials said . Affected zones included parts of the capital city of Caracas -- where streetlights were dark -- and the states of Zulia , Lara , Carabobo , Yaracuy , Portuguesa , Miranda , Falcon , Merida , Aragua , Bolivar and Tachira , the station said . Gustavo Gonzalez , the 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 do n't occur very often , '' said Javier Alvarado , president of Caracas Electricity . E-mail to a friend .
NEW : about 40 percent of power restored by about 4 p.m. local time , official says . Venezuela mayor says explosion at power station is being investigated . Power went out across much of the country 4:30 p.m . ET local time ( 7 p.m. ) High temperatures cited as a contributing factor in the outages .