Police at the scene on Friday exchanged fire with the attackers, allowing some students to run for safety, police spokesman Gambo Isah said in a statement.
Police said they would deploy additional forces to support the search and rescue. One officer was shot and wounded in the exchange of fire with the gang, they said.
Katsina is plagued by violence the government attributes to bandits – a loose term for gangs of outlaws who attack locals and kidnap for ransom. Attacks by Islamist militants are common in north-eastern parts of the country.
Violence and insecurity across Nigeria have enraged citizens, particularly after scores of farmers were killed, some beheaded, by Islamist militants in north-east Borno state late last month.
Buhari, who arrived on Friday for a week in his home village some 200 kilometres from Kankara, was scheduled to brief the national assembly on the security situation last week, but cancelled the appearance without official explanation.
