Between six and 10 militants attacked a cargo and V.I.P. area of the airport and engaged in a firefight with military personnel. One militant was also killed in the clashes.
The militants entered through an old terminal building.
Security locked down the airport and diverted flights away after the gun fire began.
Witnesses reported seeing large plumes of smoke at the airport.
No group has claimed responsibility for the attack, which resumed after a short cease fire in which Prime Minister Nawaz Sharif attempted to negotiate.