The fire broke out Friday night and quickly spread to two fuel storage areas at the illegal crude oil refinery, leaving the complex “engulfed by fires that quickly spread” in the area, said Declan Emelumba, Imo State Commissioner for Information.

The immediate cause of the explosion and the extent of deaths, injuries and damage are under investigation, Emelumba said.

“A lot of people died. The people who died are all illegal operators,” said Michael Abattam, spokesman for the Imo State Police Command. The Imo state government is also looking for the owner of the refinery where the explosion took place and has declared him a wanted person, an official said.

Illegal refineries are common in Nigeria, where shady entrepreneurs often evade regulations and taxes by setting up refineries in remote areas, out of sight of authorities.

The practice is so widespread that it affects crude oil production in Nigeria, in the oil-rich region of the Niger Delta. Nigeria is Africa’s largest producer of crude oil, but it has very few refineries and as a result most gasoline and other fuels are imported.