At least 126 people, mostly children, have been killed in a Taliban assault on an army-run school in the Pakistani city of Peshawar, officials say.
Five or six militants are said to have entered the building. Five are reported to have been killed, at least one of them in a suicide blast.
The army says most of the school’s 500 students have been evacuated. It is not clear how many are being held hostage.
The attack is being seen as one of the worst yet in Pakistan.
The BBC’s Aamer Ahmed Khan in Islamabad says the killing of schoolchildren has caused unprecedented shock.
Thousands of Pakistanis have been killed in militant violence in recent years.
A spokesman for the militants says the school was targeted in response to army operations.
Hundreds of Taliban fighters are thought to have died in a recent military offensive in North Waziristan and the nearby Khyber area.
Many of the casualties were reportedly caused by a suicide blast. At least 80 of the dead are said to be children.
The attack started at 10:00 local time (05:00 GMT). Mudassir Awan, a worker at the school, said he saw six people scaling the walls of the school.
“We thought it must be the children playing some game,” he told Reuters news agency. “But then we saw a lot of firearms with them.
“As soon as the firing started, we ran to our classrooms,” he said. “They were entering every class and they were killing the children.”
A school worker and a student interviewed by the local Geo TV station said the attackers had entered the Army Public School’s auditorium, where a military team was conducting first-aid training for students.
Locals said they also heard the screams of students and teachers. The dead are said to include teachers, as well as a paramilitary soldier.
Gunfire and loud explosions were heard as security forces hunted down the militants.
Ambulances have been carrying the injured to nearby hospitals. A helicopter is also in the area. Major roads in Peshawar in the city have been sealed off.
A doctor at the local Lady Reading hospital said many of the students were in “very bad condition”, with severe head wounds.
Frantic parents are gathering at hospitals to find out if their children are safe.
The school is at the edge of a military cantonment in Peshawar, which has seen some of the worst of the violence during a Taliban insurgency in recent years.
Many of the students were the children of military personnel. Most of them would have been aged 16 or under.
Pakistani Prime Minister Nawaz Sharif, who has just arrived in Peshawar, described the attack as a “national tragedy”.
The Pakistani opposition politician and former cricket captain Imran Khan condemned the attack as “utter barbarism”.