The attack on the school occurred in the state of Kaduna in the northwestern part of the country on Thursday evening at 23.30 local time.
The affected school is a state agricultural college located on the outskirts of the state capital.
Witnesses who spoke to the news agency Reuters say that they heard shots being fired around half past ten in the evening.
180 people could be rescued by the military early on Friday morning but about 30 students are still missing.
It concerns both men and women, says Samuel Aruwan, spokesman for the state, in a statement on Friday.
Fourth attack
Northwest and central Nigeria have in recent years been hit by an increasing number of raids by criminal gangs, which, among other things, carry out kidnappings to demand ransoms.
However, the information about these events is often incomplete and contradictory.
Thursday's attack is the fourth since December last year.
The text is updated.