Authorities are seeking the cause of a Mexico City explosion that killed 14 people and injured 100 more Thursday. The blast shook the main headquarters of Mexico’s state-owned oil company, destroying three floors and leaving 30 people stuck in the debris.

The building stands next to the famous 52-story Petroleos Mexicanos (Pemex) tower, which was evacuated as a precaution, according to the Associated Press. Several thousand people work in the Pemex tower. The explosion in the adjacent building came from the basement, and investigators speculated that an electrical problem might have triggered the devastation.

"Right now they're conducting a tour of the building and the area adjacent to the blast site to verify if there are any still trapped so they can be rescued immediately," Interior Ministry spokesman Eduardo Sanchez told a Mexican TV station.

Last September, 30 people died in an explosion at a Pemex gas plant in northern Mexico. Most accidents have occurred at pipeline installations, but before Thursday’s explosions, Pemex Operations Director Carlos Murrieta said on Twitter that the company had reduced its number of accidents in recent years.

The BBC reported that police cordoned off streets in every direction around the Pemex building as four rescue helicopters helped remove the dead and injured. Some media outlets reported defective machinery was to blame for the explosion, while Reuters quoted an anonymous ambulance driver who speculated it was a gas leak.

“I am deeply sorry for the deaths of our fellow workers at Pemex. My condolences to their relatives,” President Enrique Pena Nieto said on Twitter. “At the moment, the priority is to help the injured and protect the physical safety of those who work there.”