About 400 children in Nigeria are feared kidnapped or missing after armed men attacked a secondary school in the country's northwestern Katsina state, The Associated Press reported Monday quoting police.

Nigeria's military said they engaged men armed with AK-47s. The armed men stormed a government science secondary school late Friday. Some students climbed the school's fence and ran for safety, police said.

President Muhammadu Buhari's spokesman said government troops had surrounded the area where the bandits were believed to be holding the children captive. Police said they would deploy additional forces for search and rescue.

About 800 students are enrolled at the all-boys school in Katsina and around half remain unaccounted for. Authorities said the attackers might demand ransom.

"The bandits came on motorcycles firing and tried to enter the school. Our men, with the help of the army, engaged them in a gunfight," Al-Jazeera quoted the police saying. 

Attacks by armed bandits and Islamist militants are common in northeastern Nigeria. Katsina regularly sees groups of outlaws attacking villagers and kidnapping for money.

Human rights group Amnesty International says more than 1,100 people have been killed by armed groups in the northern part of the country in the first six months of 2020.

The abductions are the latest incident involving school children in Nigeria. More than 100 girls were kidnapped by the armed Islamist organization Boko Haram in 2018.

"The bandits will be crushed. They will be eliminated," President Buhari's representative Garba Shehu said.