More than 15,200 people have been displaced as a result of Boko Haram's attacks in a town in northern Nigeria.

Damboa – a trading centre and one of the biggest towns in Borno State - was first raided by Boko Haram on 4 July.

The Islamist insurgents raided the town again recently, and followed up with subsequent attacks.

Hundreds of people have been killed and at least 15,204 displaced.

"The number of displaced in (the town of) Biu is 10,204. We have 3,000 in Maiduguri and 2,000 in Goniri," Abdulkadir Ibrahim of National Emergency Management Agency (NEMA) told journalists. He added NEMA was struggling to calculate the death toll, due to the presence of the militants in the town.

The attacks sparked violent clashes between Boko Haram militants and security forces, who claimed they killed at least 50 rebels.

However, the Damboa vigilantes have fled leaving Boko Haram in control of the town, hoisting their flag above a public building.

The militants also cut off access to the town from the south after blowing up a bridge.

Nigeria's military tried to reassure the public about the extent of the crisis, according to news agencies Sapa and AFP.

"We are not conceding any portion of this country to any terrorist group," defence spokesman Chris Olukolade said.

"Security agencies are firming up deployment of troops in the entire area...We are also going to reverse every form of insecurity in that area very soon," Olukolade vowed.

Boko Haram opposes the westernisation of Nigeria and wishes to impose Sharia law. The group has waged a campaign of terror and violence, characterised by attacks in public spaces, such as schools and hospitals, mainly in northern Nigeria where three states - Borno, Yobe and Adamawa - have been under a state of emergency since May.

Violence linked to the insurgency has resulted in an estimated 10,000 deaths between 2002 and 2013.