At least 20 people have been killed in an explosion in Pakistan during a rally organised by an Islamist party.

Dozens of people were also injured in the explosion in north-west Bajaur district, where Jamiat Ulema-e-Islam-Fazl (JUI) was holding a meeting.

Authorities have cordoned off the area and have warned the death toll is likely to rise.

A rescue operation to assist the injured is ongoing and police have not yet confirmed the cause of the blast.

Images being broadcast on local TV show ambulances ferrying injured people to hospitals in the Pakistani tribal district of Bajaur, in Khyber Pakhtunkhwa province near the border with Afghanistan.

Some badly injured people have been waiting in the hallways of health clinics struggling to cope with the high number of casualties.

The authorities have declared a health emergency at the district hospital.

A regional leader of the JUI, Maulana Ziaullah, was killed in the blast, local officials have said.