Four female teenage suicide bombers blew themselves up, killing two people and wounding 16 others in a residential area in the northeast Nigerian city of Maiduguri on Wednesday.

The girls knocked on the door of a house and then detonated their explosive devices, a representative of the state-run emergency service in Borno State said.

The focus on individual homes is a new tactic. The attack apparently targeted a local leader.

"Community leaders should create awareness among residents not to open their doors for anybody [if] they are not aware of the visit," Borno police commissioner, Damian Chukwu, said.

Strike on Nigeria refugee camp killed at least 76

The blasts in the Muna Garage area, on the edge of the city worst hit by Boko Haram's eight-year campaign, occurred at 00:15 GMT, National Emergency Management Agency spokesman Abdulkadir Ibrahim said.

"Four female teenage suicide bombers and two other men died," he said.

Suicide bombings by teenage girls trained by Boko Haram have become a strategy of the armed group in the past couple of years. More than 200 teenage girls have lost their lives in the attacks in northeast Nigeria.

The insurgency has killed more than 20,000 people and caused a massive humanitarian crisis in the region.

The number of attacks or attempted attacks bearing the hallmarks of Boko Haram in crowded areas, such as markets and refugee camps, has escalated since the end of the rainy season in late 2016.

Most have either been foiled or the suicide bombers have only managed to blow themselves up.

Boko Haram has killed 20,000 people and displaced more than two million during its uprising in its campaign to create an Islamic state in the northeast of Africa's most populous nation.