Gunmen killed an unknown number of people and abducted four Chinese workers and some local employees after an attack at a mine in Niger state in northwestern Nigeria, the state's commissioner for internal security said on Thursday.

Niger is among states in the northwest where armed gangs are terrorising the population by killing and kidnapping people for ransom.

Emmanuel Umar said security forces had responded to a distress call on Wednesday after gunmen invaded a mining site at Ajata Aboki village in Niger's Shiroro district.

“Consequently, the joint security team engaged the terrorists and there were yet to be determined number of casualties from both sides,” Umar said in a statement.

“However, a yet to be ascertained number of workers in the mining site, including four Chinese nationals, were reported to have been abducted.”

Several people, including security personnel, are receiving treatment at a government medical facility in the state, said Umar.

It was not immediately clear who carried out the attack in Niger, where gunmen are known to carry out attacks on villages. Local officials also said last year that suspected Boko Haram militants had established a presence in Shiroro.