Half of the air traffic controllers at Sydney airport have called in sick, causing flight delays of up to one hour.

The high absentee rate slowed international and domestic arrivals and departures this afternoon, airlines said.

Qantas and Virgin Blue confirmed flights had been delayed by between 30 and 60 minutes.

A Virgin Blue spokeswoman said a number of its flights had been instructed to remain in holding patterns around the airport as they approached Sydney.

Airservices Australia (ASA), which is in charge of air traffic control, said it had three of its six controllers call in sick for the afternoon shifts.

An ASA spokeswoman said another controller had been called in to fill one of the shifts.

“This afternoon, three of our controllers from this terminal unit called in sick,” the spokeswoman said.

“We have fewer controllers than we’d have on a normal shift so we have had to reduce the number of arrivals and departures into Sydney to maintain safety.”

ASA could not comment if the high absentee rate was more than a coincidence.

“I can’t speculate about how this relates to a general shortage of air traffic controllers but we expect the situation that affects today’s delays to not be affected after this evening,” she said.

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