Suspected Boko Haram militants have carried out attacks on the city of Damaturu in north-east Nigeria, residents and security sources say.
The assault on the city, the capital of Yobe state, began shortly after 05:00 local time (04:00 GMT).
Gunshots and explosions were heard and a base of the riot police was reported to have been set on fire. Yobe State University also came under attack.
Yobe is one of three Nigerian states under a state of emergency.
The BBC spoke to a university student in Damaturu who said he had been woken by the sound of explosions and had seen a large number of militants wearing military uniforms moving into the city.
He said he and some other residents had since fled to the surrounding countryside.
‘Chaos all over’
Another resident, Umar Sada, told the AFP news agency: “We have left our homes. We are now in the bush. We don’t know what’s going to happen.”
A government official, who asked not to be identified, said: “It’s chaos all over the town. All I can hear is explosions and gunfire from my house.
“I couldn’t go out for morning prayers because this started before dawn and I’m afraid to leave in case I get caught up in it.”
Boko Haram has taken control of a series of towns and villages in north-east Nigeria in recent months.
The authorities have struggled to defeat the militant Islamist group, which has been waging an insurgency since 2009.
New York-based Human Rights Watch says Boko Haram has killed more than 2,000 civilians this year.
Boko Haram has taken control of a series of towns and villages in north-east Nigeria in recent months
On Friday, more than 100 people were killed in a gun and bomb attack on a mosque in the city of Kano.
The identity of the attackers has not been confirmed but Boko Haram has been widely blamed.
Damaturu has been targeted by Boko Haram a number of times before. At least 63 people were killed in an attack on churches and police in 2011 in what was then the deadliest attack of the insurgency.
On several other occasions since then, militants and the security forces have engaged in gun battles in the city.
Earlier this year, a suicide bomber in Damaturu targeted a crowd watching a televised World Cup football match, killing more than 20 people. (BBC News)