In a brief statement, the army said: "Rescue operation by troops underway. Exchange of fire continues. Bulk of student and staff evacuated."
The army had launched the massive military operation 'Zarb-e-Azb' in June following a brazen militant attack on Karachi's international airport and the failure of peace talks between the government and the Taliban negotiators.
The military has said more than 1,300 militants have been killed during the operation in North Waziristan and adjacent tribal region and it will continue till militancy was completely wiped out of Pakistan.
Opposition Pakistan Tehreek-i-Insaf chief Imran Khan, whose party rules Khyber-Pakhtunkhwa province, termed the attack as an act of "barbarism".