Flight QR611 to Doha was scheduled to leave Karachi at 10:25 AM. Apparently the Airbus A330 was pushed back for departure around 10:50 AM but returned to parking bay at 11:10 AM.
Some report claim the Airbus A330 experienced problem with its Auxiliary Power Unit (APU).

Source: flightradar24.com
The flight was cancelled at 12:30 PM, according to information on Karachi Airport website:

Source: karachiairport.com.pk
Passengers have been accommodated in hotel(s) in Karachi by the airline.
On June 9, Qatar Airways Airbus A330-200 aircraft registration A7-ACT arrived in Karachi at 6:54 AM as flight QR610 from Doha.

Source: flightradar24.com
Abbas