This file photo shows World Health Organization officials monitor water chlorination during a house-to-house search for new cholera cases in Mubi town, Adamawa state, Nigeria, on June 6, 2018.(Photo: Xinhua)

Nigerian authorities on Monday gathered the charred remains of over 100 people killed in an explosion at an illegal refinery in the south of the country and prepared for a mass burial after an accident described as a "catastrophe."

The blast late Friday at a site between Rivers and Imo states was one of the worst in years in an area where oil theft and illegal refining are legion, inflicting huge losses and environmental damage in Africa's largest crude producer.

Pipeline fires are commonplace in Nigeria, in part because of poor maintenance but also because of thieves who vandalize lines to siphon off oil, refine it at makeshift plants and sell the fuel on the black market.

"As at this morning, the death toll stands at 110, while many others with burns are receiving treatment in the hospitals," said Ifeanyi Nnaji of the National Emergency Management Agency (NEMA) in the area.

Nnaji said the victims were burnt beyond recognition, making it difficult for their families to identify their bodies.

"We have gathered the charred remains of the victims for a mass burial," Nnaji told AFP, later confirming the ceremony would be on Tuesday.

He said dozens of people had gathered at the site for "illegal business" before the blast that burned over 100 to death.

Burnt-out vehicles and jerry-cans used in scooping up stolen crude and petroleum products littered the scene of the carnage, he said.

Friday's incident was the latest to hit OPEC oil-producer Nigeria, which has struggled to attract new investment to its struggling petroleum industry.

The worst pipeline blast in Nigeria happened in southern town of Jesse in October 1998, killing over 1,000 villagers.

AFP