Government troops have surrounded the area where gunmen are believed to be holding schoolchildren hostage in north-western Nigeria, President Muhammadu Buhari's spokesman has said.
Ten children are reportedly being held captive, Garba Shehu said, far fewer than the number staff reported missing.
About 800 pupils were enrolled at the all-boys school in Katsina state and about half remain unaccounted for.
The attackers are thought to be seeking ransom, Mr Shehu said.
The government has blamed the attack on bandits, a loose term for gangs operating in the area.
Amnesty International says more than 1,100 people were killed by bandits in northern Nigeria in the first six months of this year, with the government failing to bring the attackers to justice.