The assailants stormed the Government Science college in the Kagara district at around 2 a.m., overwhelming the school’s security detail, according to local residents.
The state governor ordered the immediate closure of boarding schools in the area.
It was not immediately clear who was responsible for the attack.
President Muhammadu Buhari condemned the raid and dispatched security chiefs to coordinate rescue operations, his spokesman said.
Militant Islamist group Boko Haram and a branch of Islamic State are active in northern Nigeria, but kidnappings by other armed groups - mostly for ransom - are also common.
Gunmen also stormed a secondary school in northwestern Katsina state two months ago and kidnapped nearly 350 boys, who were subsequently rescued by security forces.
About 100 of more than 270 schoolgirls abducted by Boko Haram from the town of Chibok in 2014 are still missing.
Such attacks have raised concerns about rising violence by Islamist insurgents and armed gangs and fuelled widespread criticism of Buhari’s handling of national security. In January, the president appointed a new military high command.
Violence and insecurity have compounded the economic challenges faced by citizens in Africa’s most populous country, which is struggling to cope with a fall in revenues due to an oil price slump on top of COVID-19.