Security forces are enforcing a curfew in Nigeria's north-eastern town of Mubi after at least 26 people were killed by gunmen at a student hall of residence.
Most victims were students called out by name by the gunmen, police said. A resident said the attackers went from door-to-door, shooting or stabbing.
It is unclear who is responsible.
Monday night's attack came days after dozens of people with suspected links to the Boko Haram militant group were arrested in the town.
However, officials have not ruled out a recent student union election dispute as being the trigger for the violence at Federal Polytechnic Mubi.
If that proves to be the case it will shock many Nigerians, as violence amongst students has never reached this level before, the BBC's Will Ross in Lagos reports.
The college has been closed and some students fled the town on Tuesday, many with tree branches over their cars - a traditional sign of neutrality in Nigeria.
Bodies in lines
The curfew in Mubi is in place until 06:00 (05:00 GMT), police in Adamawa state said.
It said the gunmen had inside knowledge, but stressed that the motive for the attack was not yet clear.
Accounts of the attack vary - one local resident said at least 40 people had been shot dead or stabbed.
A recent attack by Boko Haram militants on mobile phone masts in the area make it hard to get information from the town.
Reports suggest men in military uniform entered a hall of residence outside the main campus shortly before midnight and gathered the students outside their rooms.
Some were shot dead and others stabbed with knives, and their bodies left in lines outside the buildings.
Some of the dead in Mubi were Muslim while others were Christian. Two security guards and an elderly resident were among the victims, the police said.
Boko Haram has not yet commented on the attack. It is fighting to establish Islamic law in Nigeria and has killed more than 1,000 people in numerous attacks across northern and central areas this year.
Adamawa state has a mixed Muslim and Christian population and borders Borno state, where Boko Haram came to prominence in 2009, staging an uprising in the capital Maiduguri.