The Airbus 310 was flying from Islamabad to Medina this evening when the incident occurred.
Civil Aviation Authority spokesman Pervez George told PTI that the pilot of flight PK-747 detected that the plane's hydraulic system had developed a fault shortly after the aircraft took off from Islamabad at about 8 pm.
The pilot reported the matter to air traffic control, which suggested he should land at Karachi airport.
"The pilot safely made an emergency landing at 9.22 pm and all passengers remained unhurt," George said.
PIA engineers were examining the aircraft.
After they submitted a report, officials would decide whether the passengers would be flown to their destination in the Airbus or another aircraft, George said.