Bacha Khan university attack in pakistan
Taliban militants attack Pakistan's Bacha Khan university killing more than 20 Reuters

At least 21 people have been killed and more than 50 injured after gunmen stormed a university campus in northwestern Pakistan and opened fire on Wednesday.

Militants entered the premises of the Bacha Khan University in Charsadda, northwestern Khyber Pakhtunkhwa province, early in the morning. They opened fire on students and teachers in classrooms and hostels.

Authorities have said four of the gunmen have been killed in encounter but many more are holed up inside the university buildings in a siege that threatens hundreds of students and teachers.

The university teaches around 3,000 students but around 600 more were participating in an event at the university when the attack took place.

Rescue workers said a professor in organic chemistry was among the killed, adding that at least 70 students were shot in the head.

Tehreek-e-Taliban Pakistan (TTP), a Taliban splinter group active in Pakistan, claimed responsibility for the attack.

In December 2014 Taliban militants had slaughtered more than 150 people in an attack on an army public school in Peshawar.

70 shot in head

The militants used the cover of thick, wintry fog and scaled the walls of the University before entering buildings and opening fire on students and teachers in classrooms and hostels, police said, according to Reuters.

"All students have been evacuated from the hostels, but militants are still hiding in different parts of the university and some students and staff are stuck inside," police inspector Wazir said.

"We are determined and resolved in our commitment to wipe out the menace of terrorism from our homeland,' Pakistan PM Nawaz Sharif said.