At least 39 people were killed and dozens more wounded Sunday by a suicide bombing at a political gathering of a leading Islamic party in northwest Pakistan, officials said.

The blast targeted the Jamiat Ulema-e-Islam-F (JUI-F) party -- a government coalition partner led by an influential firebrand cleric -- as hundreds of supporters gathered under a canopy in the town of Khar, near the Afghan border.

"The tent had collapsed on one side, trapping people who were desperately attempting to escape," said Abdullah Khan, who tried to help the victims.

"There was utter confusion, with human flesh, limbs, and body parts scattered throughout the area, alongside lifeless bodies."

Sabeeh Ullah, a 24-year-old party supporter who had his arm fractured by the blast, said the scale of injuries was horrifying.

"I found myself lying next to someone who had lost their limbs. The air was filled with the smell of human flesh," he told AFP by phone.

Riaz Anwar, the health minister for Khyber Pakhtunkhwa province, said local hospitals reported 39 dead and 123 wounded, including 17 patients in serious condition.

"It was a suicide attack, with the bomber detonating himself in close proximity to the stage," he told AFP.

Provincial governor Haji Ghulam Ali confirmed the toll.

Images from the blast site circulating on social media showed bodies strewn around the scene, and volunteers helping blood-soaked victims to ambulances.

Pakistan's national assembly is due to dissolve in the next few weeks ahead of elections expected in October or November, and political parties are already preparing to campaign.

The blast coincides with a visit by a senior delegation of Chinese officials, including Vice Premier He Lifeng, who are due to arrive in the capital later Sunday evening.