A Nigerian helicopter crashed on Monday in an area where the military is battling Boko Haram Islamists, killing two of the three people on board, a statement said, but there was no indication the chopper was shot down by insurgents.

"One of the pilots of the crashed Nigerian Air Force Mi-35 Helicopter on a training mission... has been recovered alive while the second one as well as the technician on board the 3-member crew flight died in the crash," defence spokesman Chris Olukolade said.

The rescue was "ongoing", he added.

Olukolade said the chopper crashed due to technical fault in Bama, one of the areas in the restive northeast attacked repeatedly by the Islamist insurgents waging a deadly five-year uprising.

"It is established that the crash is not as a result of any enemy action," he added.

Nigeria has been waging an offensive in the northeast since May last year aimed at crushing the Boko Haram insurgency.

The operation has been criticised as failing to significantly weaken Boko Haram, with the group relentlessly targeting civilians and the security forces across the region.

While Boko Haram is known to have anti-aircraft weapons technically capable of bringing down a helicopter, there was no immediate evidence suggesting the helicopter was brought down by force.

Bama has poor mobile phone coverage and residents were not reachable in the hours following the crash.

A Nigerian air force plane which was taking part in the regional effort against Islamist rebels in Mali crashed in Niger in May of last year while on a reconnaissance mission.