Nigerian security forces stepped up efforts Saturday to rescue dozens of abducted college students, police and officials said, as the media ran videos they said showed hostages pleading for help.
President Muhammadu Buhari meanwhile vowed an early end to the hostage crisis.
Gunmen abducted 39 students from their hostels in northwestern Kaduna state late Thursday, the latest in a series of such attacks.
The military managed to rescue 180 others after a fierce battle at the Federal College of Forestry Mechanisation in Mando at the outskirts of the state capital, Kaduna city.
"A combined team of police, army and other security forces are in a frantic search for the kidnapped students," state police spokesman Mohammadu Jalinge told AFP.
"We are combing the surrounding forests and bushes with a view to freeing the hostages. Very soon, it will be over for the bandits."
The gunmen had not made contacts with the authorities, he added.
State commissioner for internal security Samuel Aruwan said in an interview that: "An operation for the students' rescue is underway by security personnel from the army, air force, police and DSS (secret police)."
The Kaduna college targetted in the attack is reported to have some 300 male and female students -- mostly aged 17 or older.
Distraught parents, relatives and sympathisers have been arriving at the school for news.
- Buhari warns 'bandits' -
Local media meanwhile published several videos they said came from the abducted students Saturday. In one, a male student appealed to the Nigerian authorities to rescue them without violence.
The recording, purportedly sent through a Facebook account of one of the hostages, showed some of the other abducted students, male and female.
In another video, gunmen with whips were seen beating the hostages, with some wailing and pleading for mercy.
They appeared to be in a forest, surrounded by gunmen in military uniform. The video could not be independently confirmed.
In a statement Saturday Buhari warned "terrorists and bandits targeting schools", saying his government would not allow the educational system to be destroyed by their criminal activities.
He commended the early response of the military to rescue 180 students, including eight staff members.
"Our military may be efficient and well-armed but it needs good efforts for the nation's defence, and the local population must rise to this challenge of the moment," he said.
Buhari vowed "an early end to the ordeal".
Heavily armed gangs in northwest and central Nigeria have stepped up attacks in recent years, kidnapping for ransom, raping and pillaging.
They have recently turned their focus to schools, where they kidnap students or schoolchildren for ransom -- Thursday's was at least the fourth such attack since December.
Mass kidnappings in the northwest are complicating the security challenges facing President Muhammadu Buhari's security forces, who are also battling a more than decade-long Islamist insurgency in the northeast.