Militants attacked two churches in northern and central Nigeria on Sunday, spraying the congregation of one with bullets and blowing up a car in a suicide bombing at the other, hundreds of kilometres away, witnesses said.

There was no immediate word on casualties and no claim of responsibility, although attacking churches has become a trademark tactic of Islamist group Boko Haram which is fighting to reinstate an ancient caliphate in northern Nigeria.

"Three gunmen came to the premises of the church and started firing at people outside the church before going into the main building to carry on their killings ... Many people have been killed and wounded," said witness Hamidu Wakawa, who was at the church in Biu Town, in northeastern Borno state.

To the south-west, in the city of Jos, a man drove a car to the entrance of the Christ Chosen Church and then blew it up, said Emmanuel Davou, 53, who lives nearby.

Police were unable to give immediate details on either attack.

Boko Haram has been blamed for hundreds of killings in bomb or gun attacks over the past two years.

Its leader, Abubakar Shekau, frequently justifies attacks on Christians as revenge for killings of Muslims in Nigeria's volatile "Middle Belt", where Jos is located and where the largely Christian south and mostly Muslim north meet and sectarian tensions run high.

Moments after the suicide bombing in Jos, Christian youths set up roadblocks and had to be dispersed by police.

"Angry youths have gone wild, even attempting to prevent the security personnel from getting to the scene of the incident. They had to force their way out by shooting in the air to disperse them," said Davou.

Boko Haram, which has linked up with other Islamist groups in the region including al Qaeda's north African wing, has become the biggest security threat in Nigeria, Africa's top oil producer.

It usually targets security forces, although Christian worshippers are increasingly bearing the brunt.

Last Sunday, a suicide car bomber killed at least 12 people at a church in the remote northern town of Yelwa.