Police say a speeding passenger bus collided with a parked long trailer on the motorway near Khanewal where heavy fog limited visibility, killing 11 people and wounding 20 others.

A local motorway police official, Talat Mahmood, says the accident happened Thursday about 50 kilometres southeast of Multan.

Thick fog has enveloped parts of the country in recent weeks, contributing to several accidents. Deadly road accidents are common as motorists often disregard traffic laws.