Paramedics wheel an injured person to a helicopter at the parking lot of the state-run oil company Pemex after an explosion in Mexico City Jan 31, 2013. An explosion rocked the Mexico City headquarters of state oil giant Pemex on Thursday, killing at least 14 people and injuring 80 people, Interior Minister Miguel Angel Osorio Chong said on Thursday. The death toll could still rise, he told local television. The blast, which media reports said was caused by machinery exploding, occurred in the basement, emergency officials said.[Photo/Agencies]

MEXICO CITY - An explosion rocked the Mexico City headquarters of state oil giant Pemex on Thursday, killing one person, injuring more than 20 others and causing extensive damage to the building, officials said.

The blast, which media reports said was caused by machinery exploding, hit the lower floors of the building.

A local emergency official said one person died and 22 others were injured. Another four people were trapped inside the skyscraper, the official said.

"The place shook, we lost power and suddenly there was debris everywhere. Colleagues were helping us out of the building," witness Cristian Obele told Milenio news network.

Police quickly cordoned off the building and television images showed the explosion blew out windows on the lower floors and damaged the ground floor.

Interior Minister Miguel Angel Osorio Chong rushed to the scene and said he would provide details on the incident soon.

Lines of fire trucks sped to the entrance of the building near the city center and emergency workers ferried injured people through debris strewn on the street.

Pemex initially said the building had been evacuated because of a problem with its electricity supply. It then said there had been an explosion, but did not say what had caused it. Helicopters circled the building.

Plaster fell from the ceiling of the basement, and the situation at the Pemex tower was dangerous, a spokesman for local emergency services said.

Pemex has suffered a number of lethal accidents in recent years. In September, 30 people died after an explosion at a Pemex natural gas facility in northern Mexico.