An explosion at the main headquarters of Mexico's state-owned oil company in the capital Thursday killed 14 people and injured 80 as it heavily damaged three floors of the building, sending hundreds into the streets and a large plume of smoke over the skyline.

There were also reports that as many as 30 people were trapped in the debris from the explosion, which occurred in the basement of an administrative building next to the iconic, 52-story tower of Petroleos Mexicanos, or Pemex. There was no immediate cause given for the blast.

"It was an explosion, a shock, the lights went out and suddenly there was a lot of debris," employee Cristian Obele told Milenio television, adding that he had been injured in the leg. "Co-workers helped us get out of the building."

The tower, where several thousand people work, was evacuated. The main floor and the mezzanine of the auxiliary building, where the explosion occurred, were heavily damaged, along with windows as far as three floors up.

"We were talking and all of sudden we heard an explosion with white smoke and glass falling from the windows," said Maria Concepcion Andrade, 42, who lives on the block of Pemex building. "People started running from the building covered in dust. A lot of pieces were flying."

A reporter at the scene saw rescue workers trying to free several workers trapped. Television images showed people being evacuated by office chairs, and gurneys. Most of them had injuries likely caused by falling debris.

Police landed four rescue helicopters to remove the dead or injured. About a dozen tow trucks were furiously moving cars to make more landing room for the helicopters.

In an earlier Tweet, the company said it had evacuated the building as a precautionary measure because of a problem with the electrical system in the complex that includes the skyscraper. It tweeted that several workers were injured.

Streets surrounding the building were closed as evacuees wandered around, and rescue crews loaded the injured into ambulances.

Interior Department spokesman Eduardo Sanchez confirmed that an explosion in a basement garage damaged the first and second floors of the auxiliary building, which is located in a busy commercial and residential area.