At least 100 people are reported to have been killed in an attack by Boko Haram militants in northern Nigeria.

Local officials said it happened over the past two days and that 100 people were killed in the town of Baga.

Two locals said the insurgents began shooting indiscriminately and burning buildings on Tuesday evening in several raids.

They said that the militants were targeting the civilian population and that the attacks carried through to yesterday.

"They burnt to the ground all the 16 towns and villages including Baga, Dorn-Baga, Mile 4, Mile 3, Kauyen Kuros and Bunduram," said Musa Bukar, head of the Kukawa local government in Borno state.

Abubakar Gamandi, head of Borno's fish traders union and a Baga native, confirmed the attacks.

He said hundreds of people who fled were trapped on islands on Lake Chad.

Boko Haram has declared a "caliphate" in the zones it controls in northeast Nigeria.

It is also increasingly active on the borders of Niger and Cameroon.