The attack, which targeted the Jamia Masjid in Jamrud area of Khyber tribal agency, took place as people were leaving after Friday prayers. Thirty three people were killed instantly by the powerful blast, officials told the media.
Over 100 injured people were taken to hospitals in Jamrud and nearby Peshawar city, the capital of Khyber-Pakhtunkhwa province.
The officials described the condition of 20 of the injured as serious. Witnesses and officials told the media that the attack was carried out by a bomber aged about 15 or 16 years. Over 200 people were present in the mosque at the time of the blast.
A portion of the mosque collapsed and its walls developed large cracks due to the blast. Local residents dug through the rubble with their hands to pull out the dead and injured. They said some bodies could still be trapped in the debris.
Footage on television showed that the walls and ceiling of the mosque were pitted with shrapnel. Part of the ceiling was blackened by the blast and the floor was stained with blood.
A young boy wearing a blue shalwar-kameez broke down and cried as people tried to console him. No group claimed responsibility for the blast. Such attacks are usually blamed on the Pakistani Taliban.
Several militant groups, including the Taliban and Lashkar-e-Islam, are active in Khyber.