A power cut has left 70% of Venezuela without electricity, including parts of the capital Caracas.
The blackout disabled traffic lights in the city, causing traffic chaos, and partially disrupted the underground transport system.
Venezuelan President Nicolas Maduro blamed the opposition for "sabotage" to power transmission lines but critics say poor management and the failure to invest in infrastructure are to blame, the BBC reports.
Authorities say they are working to re-establish services, and they will give priority to transport in Caracas.
The oil industry has not been affected by the power cut, as Venezuela's oil refineries are powered by separate generator plants.
In 2010 the late President Hugo Chavez signed a decree declaring an "electricity emergency" to help his government tackle power shortages, the BBC says.
Although Venezuela has big oil reserves, it is dependent on hydro-electricity for some 70% of its power.