An explosion at a Simec-owned steel plant in Mexico’s central Tlaxcala state early Wednesday killed at least 12 people, state authorities said.

“At the plant of the steel complex located in the city of Apizaco, Tlaxcala, there was a spill of liquid steel with the loss of human life, temporarily paralyzing operations,” the company said in a statement.

Simec said they are investigating the cause of the crash.

The state civil protection office said in a social media post that the explosion was likely caused after the melter collapsed.

Those killed were factory workers, the prosecutor’s office told Reuters. One person is hospitalized in critical condition, the office added.

Authorities say they are investigating the cause of the incident. However, molten steel, when it comes in contact with water, causes an explosion.