ABUJA, Nigeria (AP) — More than 50 people have been killed and many wounded in southeast Nigeria in an explosion that rocked an illegal oil refinery, state officials and the police said Saturday.

The death toll may be more than 100, according to a report in the Lagos-based Punch newspaper. The fire is reported to have spread to nearby properties.

The fire broke out on Friday night and quickly spread to two fuel storage areas located at the illegal crude oil refinery causing the complex to be “engulfed by fire which spread rapidly” within the area, said Declan Emelumba, Imo State Commissioner for Information.

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

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

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

The practice is so widespread that is it affecting Nigeria's crude oil production, in the oil-rich Niger Delta region. 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.