A bomb strapped to a girl aged about 10 years old exploded in a busy market place in the Nigerian city of Maiduguri on Saturday, killing at least 19 people and injuring more than 20, security sources say.

The powerful explosion rocked the market at about 12:40pm (local time) when it was packed with shoppers and traders.

Borno State police spokesman Gideon Jubrin told reporters: "Casualty figure: 20 dead and 18 injured, including the female suicide bomber that detonated the improvised explosive device."

The same market was hit twice by female suicide bombers late last year.

There was no immediate claim of responsibility but Boko Haram militants have increasingly used women and young girls as human bombs in their six-year quest for a hardline Islamic state.

Civilian vigilante Ashiru Mustapha said the explosives detonated as the girl was being searched at the entrance to the market.

"The girl was about 10 years old and I doubt much if she actually knew what was strapped to her body," he told the AFP news agency.

"In fact, she was searched at the entrance of the market and the metal detector indicated that she was carrying something.

"But sadly, the explosion went off before she was isolated, killing at least 10 people and injuring many others."

The market was cordoned off as health officials began the grim task of sifting through the wreckage and collecting body parts.

A Red Cross official, who declined to give his name, said 10 bodies had been taken to the mortuary at the Borno State Specialist Hospital.

"Many people sustained life-threatening injuries," he said.

An attack at the market on December 1 killed more than 10 people, and the previous week more than 45 people lost their lives in an attack there.

Boko Haram launched its first female suicide attack in June last year in the northern state of Gombe and there have been a spate of bombings since, including four in a week in the city of Kano.

In July, a 10-year-old girl was found in Katsina state wearing a suicide vest, prompting speculation that young girls were being forced into becoming human bombs rather than through ideological motivation.

AFP