A policeman stands near damaged vehicles in Sabon Gari, Kano May 19, 2014.[Photo/Agencies]

JOS - Back-to-back bomb blasts killed at least 118 people and wounded 45 in the crowded business district of the central Nigerian city of Jos on Tuesday, emergency services said, in an attack that appeared to bear the hallmarks of the Boko Haram insurgents.

There was no immediate claim of responsibility. But the militant group Boko Haram, which has set off bombs across the north and centre of Nigeria in an increasingly bloody campaign for an Islamic state, was likely to be the prime suspect in what would rank among their deadliest single attacks in five years of insurrection.

Boko Haram grabbed world headlines by abducting more than 200 schoolgirls on April 14 from the northeastern village of Chibok. Britain, the United States and France have pledged to help rescue them.

If the Jos attack was the handiwork of Boko Haram, it would show their growing reach in Africa's top oil producing and most populous country, striking out beyond their heartland in Nigeria's semi-arid and weakly governed northeast. Several bombs have exploded outside that region over the past month.

It was also likely calculated to stoke civil strife in Nigeria's most combustible ethnic and sectarian tinder box. Jos and the surrounding Plateau state have seen thousands killed in tit-for-tat violence between largely Christian Berom farmers and Muslim Fulani cattle herders over the past decade.

A Reuters reporter saw 10 bodies burned beyond recognition at the bomb site opposite a hospital at Terminus, the downtown area of Jos which houses shops, some offices and a market.

"We've now recovered 118 bodies from the rubble," said Mohammed Abdulsalam, coordinator of the National Emergency Management Agency in Jos. "This could rise by morning, as there is still some rubble we haven't yet shifted."

Plateau state Police Commissioner Chris Olakpe earlier confirmed a death toll of 46, adding that other wounded had been taken to hospital.

"The first explosive went off around 3 p.m. The second was about 3:30 while people gathered to help the victims," he said by telephone. "This is a very busy area of Jos metropolis."

The back-to-back blast tactic, whose aim is to maximise civilian casualties, has also been used by militants in Iraq and other places.

Jos has been relatively free of attacks by Boko Haram, but it claimed responsibility for a bomb in a church in the highland city, as well as two other places, on Christmas Day in 2011.

The city is in the heart of Nigeria's volatile "Middle Belt", where its largely Christian south and mostly Muslim north meet, and surrounding Plateau state is often a flashpoint for violence, although the Christmas bombing failed to trigger any.

But in a sign it could, a mob of Christian youths armed with clubs advanced toward a Muslim part of Jos before police held them back, police spokeswoman Felicia Anselm said by telephone.

"The Christians were advancing toward us and I thought I was going to die," Dalami Aspar, who escaped a mob as they ran toward him in the street, told Reuters.

"Cruel and evil"

President Goodluck Jonathan condemned the blasts, calling the perpetrators "cruel and evil."

"The government remains fully committed to winning the war against terror, and this administration will not be cowed by the atrocities of enemies of human progress and civilization," he said in a statement emailed by his office.

He announced heightened measures to tackle the insurgents, including a multinational force around Lake Chad, comprising a battalion each from Chad, Niger, Cameroon and Nigeria.

Tuesday's explosions burned several shops to the ground, shattering windows and spreading rubble in the road. Police sirens wailed as officers rushed to the scene.

"There was a loud bang that shook my whole house. Then smoke was rising," said Jos resident Veronica Samson. "There were bodies in the streets and people rushing injured to hospital in their cars."

For most of the past two years, the insurgency has been largely confined to Nigeria's remote northeast bordering Cameroon, Chad and Niger, where militants move easily across borders, but it appears once again to be spreading outward.

A morning rush hour bomb killed at least 71 people at a bus station on the outskirts of the capital Abuja last month. Another in almost exactly the same place, in the suburb of Nyanya, killed at least 19 people at the beginning of May.

A suicide car bomber also killed five people in the northern city of Kano on Sunday evening in an area mostly inhabited by southern Christians.