A power outage left at least 40 percent of Venezuela without electricity on Tuesday, including much of the capital.

Between 40 percent and 50 percent of Venezuela’s territory was affected by the late-afternoon outage, said Gen. Hipolito Izquierdo, president of the national electric corporation.

Power returned to downtown Caracas after about an hour and a half. It was unclear how soon power would be re-established in other areas. Izquierdo said the problem was being resolved.

The blackout caused stoplights to stop functioning and temporarily forced the closing of the Caracas subway. Workers emerged from darkened buildings.

The outage was caused by a failure of the transmission system near the Guri hydroelectric dam in eastern Venezuela, said Javier Alvarado, president of the state utility Electricidad de Caracas, on state television.

The initial failure set off a chain reaction during peak power consumption hours on a hot day, Izquierdo said.

It was unclear if the outage had affected Venezuela’s oil industry.