A blackout has cut power to much of Venezuela including Caracas and other major cities, and interrupting a televised speech by the president in the country's second nationwide electricity outage in a year.
The blackout affected Caracas for about three hours, but power was gradually restored by early evening and underground metro trains were running again. Venezuela's second city, Maracaibo, was also hit.
President Nicolas Maduro said it was not clear what led to the "strange" incident in a television address.
"We are going to investigate thoroughly and objectively ...The causes will be known because, be aware, there are no reasons linked to the service itself. There was not more demand than supply ... it was not peak hours," he said.
An outage at a power station in the centre of the country led to other generation centres going offline and disrupting the supply across a broad swath of the Andean nation, Electricity Minister Jesse Chacon told state television.
The OPEC nation has suffered an increasing number of blackouts in recent years, which critics have attributed to low electricity tariffs and limited state investment following the 2007 nationalisation of the sector.
The blackout came mid-afternoon as Maduro was speaking during a broadcast of the awards ceremony for a national journalism prize, Reuters news agency reported.
Officials said they would prioritise Caracas as they restored power to all states, AP news agency reported. The last time Caracas lost power, in March, electricity was not fully restored for 12 hours.
The government attributed the last nationwide blackout in December on saboteurs attacking infrastructure.
Maduro this year weathered three months of often violent opposition demonstrations demanding his resignation. He said the protests were a US-backed attempt to overthrow him.
A spokesman at state-run oil company PDVSA said there were no reports of any impact to the country's 2.9 million barrel-per-day petroleum industry.