Power returned slowly to Venezuela 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.

“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, said Juan Barreto, mayor of Caracas.

“That produced a blackout in 16 states of the country, particularly those of the central north coastal area.”