An explosion rocked the Mexico City headquarters of Mexican oil giant Pemex on Thursday, killing at least 14 people and wounding 80 more as rescuers sifted through debris for survivors.

People were carted away on stretchers and office chairs, as a huge plume of smoke billowed toward the sky. Heavy damage was visible to the 54-story building's ground floor. Emergency workers, helicopters and several ambulances were at the scene.

"We have 13 dead at the scene and one more at the hospital. There are more than 80 wounded and we continue to look for survivors in the debris," Interior Minister Miguel Angel Osorio Chong told reporters.

A spokesman for the civil protection agency told AFP that the blast was caused by "an accumulation of gas" in an electrical supply room of the tower's lower floors.

Pemex said on Twitter that the blast hit the ground floor and mezzanine.

Some witnesses told local media that a number of people were trapped in rubble.

"It was dramatic. The building was shaking and suddenly there was debris. We couldn't even see the people next to us," Pemex employee and union member Cristian Obele told reporters.

Another worker told the Televisa channel that the "very strong explosion" took place around 4:00 pm (2200 GMT).

"Windows broke, people were injured and a lot of people were in shock," the unidentified worker said.

Mexico's President Enrique Pena Nieto and the capital's Mayor Miguel Angel Mancera headed to the scene of the accident. Authorities closed off the avenue in front of the tower.

Pemex, the world's fourth-largest producer of crude with around 2.5 million barrels per day, announced earlier that it had evacuated the building due to a power failure.

The company has experienced deadly accidents at its oil and gas facilities in the past. Last year, a huge explosion killed 30 people at a gas plant near the northern city of Reynosa, close to the US border.

The previous worst incident took place in December 2010, when an oil pipeline exploded after it was punctured by thieves in the central town of San Martin Texmelucan, leaving 29 dead and injuring more than 50.

In October 2007, 21 Pemex workers died during a gas leak on an oil platform in the Gulf of Mexico. Most drowned when they jumped into the sea in panic.