One person was killed and 20 others injured here Thursday in an explosion at the headquarters of state-owned oil monopoly Petroleos Mexicanos, Mexican media outlets said.

The blast was apparently caused by an electrical fault, according to those accounts.

The entire B2 building at the Mexico City headquarters complex was evacuated as a precaution, Pemex said on Twitter.

The explosion was very powerful, an injured employee told Efe at the scene. He said several co-workers told him about another person who lost his legs in the blast.

"There are injured," Pemex said in a second tweet, providing no details.

Unnamed first responders told the Milenio network that at least one person was killed and Televisa television also reported a fatality, but officials have yet to say anything about casualties.

Police and soldiers cordoned off the area around the Pemex headquarters. EFE