Ten planes had to circle in the air

Another replacement controller was held up in traffic.

Pilots of circling planes were informed and takeoffs were delayed as air traffic control was shut down, officials said.

The incident has raised concerns about cuts in staffing of air controllers.

Warning issued

Airways Corporation, which manages air traffic control, said the organisation had put out a warning the previous evening.

Describing the incident as extremely rare, its chief operating officer Ashley Smout said there was no danger when planes were unable to land.

There have been cuts in staffing

However, there are concerns that if any aircraft needed to make an emergency landing, they would have received no help from the control tower.

"If someone had to land in a big hurry they had all the normal instruments and other approach aids to land with," Mr Smout said.

Staffing problems

Airways Corporation said two staff two were sick at short notice while another two had long-term illnesses.

But a report by the New Zealand Herald, which spoke to some personnel, said staffing levels at the airport had been reduced to critical levels.

Air traffic controllers are coping with rising numbers of planes

Even normal staff problems could not be covered sometimes, the newspaper reported.

One worker, who asked not to be named, said the airport could have been shut down for two-and-a-half hours in the afternoon, had anyone else fallen sick.

"[This] goes back 18 months to when Airways Corp centralised in Christchurch and people were made redundant," the Airways staff member said.

"The effect is pretty dire - where there used to be three, there is now one."

One pilot also claimed no warning was issued the previous night, the paper reported.