Hundreds of schoolgirls are feared to have been kidnapped in the north-western state of Zamfara.
A teacher told the BBC that at least 300 students were unaccounted for after the Friday morning attack by gunmen.
A spokesman for the state’s governor has confirmed the attack but did not give details.
This is the latest mass abduction targeting schools in recent weeks. Armed gangs often seize schoolchildren for ransom.
At least 42 people, including 27 students, who were kidnapped last week in Kagara, in the neighbouring Niger state, are yet to be released.
In December, more than 300 boys were kidnapped by gunmen in Kankara in Katsina state and later released after negotiations.
But the 2014 kidnap of 276 schoolgirls in the north-eastern town of Chibok by Islamist militants Boko Haram brought global attention to the mounting security challenges Nigeria was facing.
How did the attack happen?
Friday’s attack happened at 01:00 local time (midnight GMT) when a group ofgunmen arrived at the Government Girls Secondary School in Jangebe town with pick-up vehicles and motorcycles, a teacher told news site Punch.
Some of the gunmen were dressed as government security forces, the report said, adding that they forced the schoolgirls in the vehicles.
But other witnesses have told the BBC that the armed men arrived on foot at the school.
Worried parents have gathered outside the school and some have gone out into the bush to look for their daughters, witnesses say.
A teacher told the BBC that of 421 students in the school at the time, only 55 had been unaccounted for, meaning more than 300 were believed to have been kidnapped.
Why are schoolchildren being abducted?
Every time children are taken from their schools by armed gunmen in northern Nigeria, the kidnapping of the Chibok girls is mentioned.
Similar raids took place before that well-publicised abduction but they received little publicity and they never involved girls.
But the publicity that incident generated showed armed groups that the mass abduction of children was a sure way of applying pressure on authorities, including asking for ransom, although the authorities always deny paying.