Fighters from the Islamist militant group Boko Haram have launched an attack on the key city of Maiduguri in north-eastern Nigeria, reports say.
Fierce fighting was reported on the outskirts. The military is carrying out air strikes, and a curfew is in place.
Maiduguri is home to tens of thousands of people who have fled Boko Haram attacks and was visited on Saturday by President Goodluck Jonathan.
Another Boko Haram attack was reported in Monguno, north of Maiduguri.
Boko Haram, which means “Western education is forbidden” in the Hausa language, launched military operations in 2009 to create an Islamic state.
Thousands of people have been killed, mostly in north-eastern Nigeria.
Separately, US Secretary of State John Kerry is scheduled to arrive in Lagos on Sunday.
‘Pray for us’
Residents of Maiduguri, the capital of Borno state, say they woke to sustained loud explosions and gunshots. Roads and business have been closed by security forces.
The attack appeared to have begun in the Njimtilo district on the edge of the city.
One resident there, Rachel Adamu, told Reuters: “Please pray for us, we are in danger, under serious attack now.”
A resident of the Moronti area, Buba Kyari, told Agence France-Presse: “It is flying bullets everywhere. All we hear are sounds of guns and explosions. A rocket-propelled grenade hit and killed a person from my neighbourhood who was fleeing into the city.”