All flights out of Sydney Airport were delayed on Monday morning due to a radar failure at air traffic control with a reduced amount of arrivals and departures commecning after the outage.
Hundreds of passengers have been affected after the "technical issue" hit around 5am on Monday, on the first day of the NSW schools holidays.
"All flights at Sydney Airport are currently grounded until further notice due to an Air Traffic Control issue," a Virgin spokeswoman told AAP.
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Sydney Aiport advised if people are travelling on Monday people should check with the airline for further information.
Qantas, Virgin Australia and Jetstar have confirmed the problem is affecting flights.
Virgin Australia said it would try to get all of its passengers on their way as quickly at it can after the problem is fixed.
"We will be contacting those guests who may be impacted but we encourage all guests to check the flight status page," the spokeswoman said.
Airservices Australia, which manages airport traffice control, confirmed there was an "issue".
"At this stage we do have a confirmed technical issue at Sydney which we are trying to rectify. We are also managing flights safely," Air Services Australia spokeswoman, Sarah Fulton told AAP.
Power in the traffic systems operations went down and air traffic control has had to revert to a manual process for departing flights, at a reduced rate, AAP understands.
Passengers at the airport have tweeted photos of a departures board with flight status reading "delayed - due ATC radar failure".
"Flights are delayed due to an @airservices system issue. Please check with your airline for flight status. Thanks for your patience", Sydney Airport tweeted.
Power in the traffic systems operations went down around 5am on Monday, AAP understands.
Sydney Airport tweeted that the technical issue has been resolved.
