MEXICO CITY (AP) — State-owned oil company Petroleos Mexicanos says an explosion has occurred at its Cadereyta refinery outside the northern city of Monterrey.

Pemex spokesman Leon Mario Alzas says authorities are still trying to determine the cause, the extent of the damage and if anyone was hurt.

Mexican media report that several people have died in Tuesday's explosion, but Alzas says he cannot confirm that.

Cadereyta is one of Mexico's most important refineries, with a capacity of 235,000 barrels a day.