The aircraft, which was going from Karachi to London, had 167 passengers and 16 crew members on board.
The aircraft turned back to Karachi airport and landed shortly after noon.
Officials of the Civil Aviation Authority sought to play down the incident and said the pilot had landed after one of the engines developed a technical fault.
TV news channels said the pilot had landed on one engine and that all persons on board were safe.
PIA made arrangements to send the passengers to London on another aircraft.
Pakistan's national carrier has been plagued by a funds crunch and reports of poor maintenance of its fleet.
PIA flights are regularly delayed, causing inconvenience to travellers.