BEIJING (AP) — Twelve people are missing following an explosion at a chemical plant in northern China.

The official Xinhua News Agency says 13 people were on a floor that produced emulsion explosives at the plant run by Kailuan Group in the city of Tangshan when the blast occurred Friday morning.

Xinhua says one person was rescued and that authorities are searching for the 12 others. It gives no cause for the explosion.

Workplace safety is a major issue in China. A shoe factory fire in the eastern city of Wenling in January killed 16 people, prompting a broad governmental check on compliance of safety rules.

Last June, 121 people were killed in a poultry plant fire in northeastern China, and investigators found that the plant’s safety exits had been blocked, trapping workers.