At least 33 people have been killed in a suspected suicide bomb attack in northwest Pakistan.

The bomb went off on a main road near the city of Kohat, 150km southwest of Islamabad, and brought down some roadside shops and other buildings.

A police spokesman said around 80 people were wounded.

Residents spent hours sifting through the wreckage, which occurred a couple of days before the Eid al-Fitr, end-of-Ramadan holiday.

Among the dead were workers waiting to catch buses home for the holiday.

The area where the attack took place is mostly inhabited by minority Shia Muslims and there has been sectarian violence in the region in the past.