At least 10 people were injured in a blast at the election office of a Pakistan Tehreek-i-Insaf (PTI) candidate in Razmak tehsil of North Waziristan tribal district on Tuesday, officials said.

“A huge explosion happened when I was inaugurating my election office in Razmak city,” Malik Aurangzeb Khan, PTI's candidate from NA-48 in the region bordering Afghanistan, told AFP.

“At least 10 people were injured in the blast,” he said, adding that he could not confirm the nature of the explosion.

A local administration official told AFP on condition of anonymity that an unidentified person threw a grenade at the gathering. A security source also confirmed the attack.

Sources said panic ensued after the attack and the injured were crying for help.

"Around 100 to 150 supporters of Malik Aurangzeb were present at the time [of the blast]," a local resident told DawnNewsTV.

A large number of people suffered minor injuries in the grenade attack, while 10 people with major injuries were shifted to a nearby hospital, a source said.

There was no immediate claim by any militant groups for the blast.

North Waziristan is one of Pakistan's seven tribal districts bordering Afghanistan, a region long rife with militancy.

But the Pakistan Army has conducted a series of operations there in recent years and claims to have flushed the militants out, with the region set to be merged with Khyber Pakhtunkhwa.