Mexico City, Mexico (CNN) -- An explosion Thursday at a Mexican electrical substation injured 12 people, most of them firefighters or other rescue personnel, the state-run news agency reported.
The explosion occurred in Mexico City's historic district around 6:30 a.m. (8:30 a.m. ET), the Notimex news service reported.
The explosion occurred when a fire at the substation came in contact with fuel at the facility, officials said. But authorities did not immediately say what caused the fire.
Eight firefighters were injured, as were an auxiliary police officer, an emergency and rescue squad worker and two employees from the Federal Electricity Commission, Notimex said, citing Elias Moreno Brizuela, an official with Mexico City's civil protection agency.
The injured were taken to hospitals but none are in grave danger, Moreno said. Most of them suffered burns on their faces and hands, the official said.