At least 18 people, including a pregnant woman, have died in southern Nigeria when an illegal oil refinery exploded into flames, a security official and residents said.

Iran PressAfrica: The blast happened on Monday in the southern River state’s Emohua district, where illegal refineries are common. Residents said the death toll was likely to grow because many of the bodies were completely burned and dozens of people were injured.

Police confirmed the incident but did not provide details of what happened. Locals said most of the people who died had worked at the illegal refinery in the village of Rumucholu.

Dozens of people were being treated in hospitals, he said. A pregnant woman was among the 15 victims confirmed dead, according to a statement issued by the Youths and Environmental Advocacy Centre, a local environmental rights group.

Explosions at locally run refineries are common in the oil-rich but impoverished Niger Delta region, where most of the nation’s oil facilities are targeted by chronic oil theft.