A large explosion has rocked a bus station in a northern region of Nigeria previously targeted by Boko Haram, witnesses said, in what appeared to be the latest crack in the government's purported ceasefire with the armed group.

"We had a huge blast at exactly 9:45pm (20:45 GMT)... We realised it had come from the bus station," said Musa Babale, a resident of the town of Azare in Bauchi state where the blast occurred on Wednesday.

"The whole place was a mess," he added, in an account supported by several others.

The police and military did not answer calls seeking comment but another resident of the affected area near the Kano road said the security forces had surrounded the site.

"We found the place cordoned off by soldiers and police," said witness Mauzu Ibrahim. "From where I stood I saw bodies being put in a van."

Other witnesses also reported seeing casualties but it was not immediately possible to estimate the number and emergency workers were not available to comment.

While the cause of the blast remained unclear, and no group has claimed responsibility for the attack, Bauchi has been one of the hardest hit areas in Boko Haram's five-year uprising against the Nigerian state. 

Bus station bombings have also become something of a hallmark for the armed group, after twin attacks at a terminal on the outskirts of the capital Abuja earlier this year killed nearly 100 people.

The station in Azare, a town roughly 200-km from the state capital Bauchi city, is a widely used transit point by travellers coming from Nigeria's embattled northeast, which has been under a state of emergency since May of last year.

Azare saw a series of attacks blamed on Boko Haram through 2012, while Bauchi has been consistently targeted throughout the uprising, including through church bombings, coordinated gun raids and notably a massive prison raid in 2011.

Last Saturday, Nigeria claimed to have reached a deal with the armed rebel group, but continued violence following the agreement was announced raised doubts about the purported breakthrough.

Boko Haram, which wants to create an Islamic state in mainly Muslim northern Nigeria, is a fractured group with an unclear command structure.

Analysts doubt that the individuals in talks with Nigeria have the influence to enforce a blanket ceasefire.

Source: AFP