Witnesses say at least 20 people are dead and many others are missing after suspected extremists ambushed a military and civilian convoy in Nigeria's northeast.

The witnesses say the military was relocating civilians to a displacement camp in Damboa on Saturday morning when the ambush occurred.

The Boko Haram extremist insurgency has long been active in the region.

A driver told The Associated Press he saw about 20 bodies and many burned-out vehicles. Another survivor said the convoy contained hundreds of civilians and a few dozen soldiers but only a few people reached Damboa.

The fate of the others was not immediately clear. Both witnesses spoke on condition of anonymity out of fear for their safety.

Army spokesman Sagir Musa did not immediately respond to calls for comment.