A Nigerian state government said it was negotiating with gunmen who seized 136 children from an Islamic seminary at the weekend, the latest in a string of mass kidnappings in the country. 

Criminal gangs have often targeted schools in remote areas, where pupils live in dormitories with little security protection, before hauling their victims into nearby forests to negotiate ransoms.

Police said gunmen attacked Tegina town in Niger state on Sunday, arriving on motorbikes and shooting indiscriminately.

Niger state police said the criminals killed one resident, injured another before kidnapping children from the Salihu Tanko Islamic school.

"We are in touch with the kidnappers to find a way to secure the release of the children. We are negotiating to see how we can arrive at an agreement," deputy governor Ahmed Mohammed Ketso told reporters on Wednesday. 

"We are also in contact with the parents. We call on them to be patient, government is making all efforts to secure the release of the children."

Ketso also confirmed 136 students had been taken. 

President Muhammadu Buhari has ordered security forces and intelligence agencies to step up efforts to rescue the children.

Buhari "condemned as unfortunate" the kidnapping of children, according to a statement from his spokesman Garba Shehu, and urged all those involved in the rescue operation to do their utmost in securing their immediate release.

The attackers did release 11 of the pupils who were "too small and couldn't walk" very far, the authorities previously said.

Niger's deputy governor said the government did not pay ransoms, adding that security agencies were "being careful in the pursuit of bandits to avoid collateral damage."

Relatives of the kidnapped schoolchildren appealed to the government to help free them.

"My appeal to the government is that they should try to protect our people first and our children first," Sa'idu Umar, whose child was among those abducted, told AFP.

"We are hoping that they are going to try harder to bring back our children successfully."

Mothers and other relatives crouched, weeping and waiting for the missing children outside the school on Tuesday.

Armed gangs are terrorising inhabitants in northwest and central Nigeria by looting villages, stealing cattle, and taking people hostage. 

More than 700 children and students have already been kidnapped by gunmen for ransom since December.

Mass kidnappings in northwest and central Nigeria are complicating challenges facing Buhari's security forces, who are also battling a more than decade-long jihadist insurgency in the northeast of the country.