At least 37 people have died in Nigeria while attempting to steal oil, according to an environmental group.

The Youths and Environmental Advocacy Centre said the incident took place in Rivers state on Thursday, and saw the victims attempt to siphon crude oil from a vessel to their boats from an "illegal tapping point".

It resulted in them inhaling toxic fumes at high pressure, it said.

Many are still missing, according to the report, which quotes a network of volunteers.

Nigerian police confirmed the incident took place, but gave no further details, and added that an investigation was under way on Friday.

"The Rivers state police command can confirm the deaths. The victims were allegedly attempting to steal crude oil," said spokesperson Blessing Agabe.

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Oil theft is common in the Niger Delta region of Nigeria, Africa's biggest oil producer, where decades of oil exploration have led to high levels of poverty and environmental degradation.

The Nigerian government said oil theft causes several billion dollars in losses annually and has been clamping down on the practice.

Speaking to Sky News in 2017, some oil thieves operating in the area said that they wanted to be seen as legitimate.

One person calling himself Emo, who said he employed nearly 2,000 people, told Sky's special correspondent Alex Crawford: "There are no jobs. We have nothing to do. You understand?

"That is why we are seeking help. We are begging for the government to assist us. You understand? We know what we're doing is wrong but we have no option."