At least three soldiers, six vigilantes and dozens of Boko Haram insurgents have been killed during clashes in the restive northeast Nigerian city of Maiduguri, sources said on Thursday.

The Islamist militants launched an attack on the Borno state capital on Wednesday evening but were repelled by Nigerian troops after intense fighting, residents and the army said.

The assault was the first on Maiduguri for three months and came after sweeping offensives against Boko Haram strongholds by a regional military coalition of Nigeria, Niger, Chad and Cameroon.

"Three soldiers were killed during a fight with the terrorists while six of our members were killed by three female suicide bombers," civilian vigilante official Yusuf Sani said on Thursday.

"The terrorists suffered serious casualties," he said, without specifying a figure, adding that 12 vigilantes were injured by the shrapnel of the detonated bombs.

An army official, who did not want to be identified because he is not authorised to speak to the media, confirmed Sani's account.

"We rounded them and killed many of them... I cannot tell you the number of we killed them," he added.

The army imposed a dusk-to-dawn curfew on Thursday in the aftermath of the attack.

Streets were deserted and only soldiers and police were seen patrolling. Schools, markets and public buildings, including hospitals, were also closed, an AFP reporter in the city said.

Army spokesman Colonel Tanko Gusau said the lock-down was ordered "to protect lives and properties of innocent and law-abiding people of Maiduguri".

The attack saw dozens of militants armed with heavy guns and rocket-propelled grenades storm the northern outskirts of the city near the Giwa military base.

Shots were fired and explosives detonated indiscriminately, locals said.

The army said female suicide bombers had detonated explosives before the attack.

Sources said the assailants had made attempts to overrun the military facility, which was attacked on March 14 last year, freeing hundreds of detained Boko Haram suspects.

A member of the civilian vigilantes, who assist the military with security and intelligence, said the attack could have been a reprisal for losses incurred in a Tuesday offensive on their camp some 40 kilometres (25 miles) outside Maiduguri.