Several blasts and gunshots were heard late on Sunday inside a Pakistan Air Force base in Karachi, the country's largest city, the police said as interior minister Rahman Malik confirmed it as a terrorist attack.
"Several blasts were heard inside, the firing is still continuing," Aslam Khan, a senior police officer at site said.
The blasts and firing began at about 10.40pm in the naval section of the Shahrahe Faisal airbase, witnesses were quoted as saying by TV news channels.
Dawn News channel quoted witnesses as saying that they had heard up to five blasts.
Heavy firing continued over 20 minutes after the first blast occurred. Geo news reported that the explosions took place in the guardroom of the base.
Ambulances were seen rushing to the airbase as security guards cordoned off the area.
The high-security area houses the PA's Southern Air Command, Air War College and museum as well as PNS Mehran, the main naval air station in Karachi.