One news report has said that the CHC ATC tower has collapsed but I cant find any other reports to collaborate. The below is snipped from Stuff website (sorry can post links :-()
"Flights in New Zealand are not taking off in the wake of today's 6.3 magnitude earthquake in Christchurch.
Auckland Airport spokesman Richard Llewellyn said the airways system around the country was closed shortly after the earthquake.
"For the moment planes are landing but no planes are departing,'' he told NZPA.
"The national air traffic control centre is in Christchurch, and they are checking to make sure it is all okay, and until then the airways system has been closed."
Air New Zealand says flights in and out of Christchurch have been cancelled until at least 7pm."