The explosion in the crowded Noor market of Parachinar town in the province came as people gathered for Friday prayers near the women's entrance to a Shia mosque.

Security forces cordoned off the area. The administration declared an emergency at all hospitals. 

An army helicopter was flown to Parachinar to evacuate the injured, the Inter-Services Public Relations said.

The area where the blast took place borders Afghanistan and was once the main route for cross-border militant activity.

Prime Minister Nawaz Sharif condemned the attack and said the government would step up efforts to "eliminate the menace of terrorism".

"The network of terrorists has already been broken and it is our national duty to continue this war until the complete annihilation of the scourge of terrorism from our soil," he said.

Pakistan Tehreek-i-Insaf chief Imran Khan also denounced the killings.

In January, at least 25 people were killed and over 65 injured when a powerful explosion took place in the same region.