Scores are dead after vicious weekend clashes in central Nigeria between mostly Muslim cattle herders and Christian farmers, with one report citing police saying 86 people were killed.

The growing conflict by some accounts has become deadlier than Nigeria's Boko Haram extremist insurgency.

Dramatic footage from Jos showed angry people waving machetes and sticks and shouting at passing security forces as they weaved around overturned and burning vehicles. Smoke rose in the distance. Women and children clutching overstuffed bags piled into the back of trucks, seeking a way out.

President Muhammadu Buhari warned against reprisal attacks after the "deeply unfortunate killings across a number of communities" in central Plateau State as the military and police tried to end the bloodshed, saying "no efforts will be spared" to find the attackers.

Nigeria's government has not announced a death toll. The independent Channels Television cited a Plateau State police spokesman, Mathias Tyopev, as saying 86 people had been killed, with at least 50 houses destroyed.

"Please remain calm," said the Plateau State governor, Simon Bako Lalong, as a helicopter whirred overhead. "It is very, very, unfortunate that an incident is happening again like this."

The deadly clashes between herders and farmers in central Nigeria are a growing security concern in Africa's most populous country, which is roughly split between Muslims in the north and Christians in the south.

Thousands flee Boko Haram to camps in Niger

The threat from Boko Haram, which continues to carry out attacks in the northeast, has been cited as one cause of the growing tensions as herders — also feeling the effects of climate change — are forced south into more populated farming communities in search of safe grazing.

The widespread security issues pose a major challenge to Buhari, a Muslim former military ruler who won office in a democratic transfer of power in 2015, as elections approach next year.

While few details emerged immediately of the latest killings, Nigerians on social media shared a growing sense that something awful had occurred for hours on Sunday.

Earlier in the day, the Plateau State governor announced a 6pm to 6am curfew after saying he had woken up to the "shocking news" of the attacks. He said the curfew affects the communities of Jos South, Riyom and Barkin Ladi "and is in effect until further notice".

"Observe the curfew, observe the curfew, and I will still remind them to observe the curfew," he said.