AN air traffic control system fault has grounded flights trying to depart Sydney airport.
Frustrated passengers who arrived for early flights have been told a "nationwide system fault" is preventing all flights from leaving Sydney.
News.com.au understands a system used by Air Services Australia has been disrupted, affecting departures out of the airport.
Arrivals are not believed to been affected, despite passengers at the airport reporting they have been told otherwise.
Passengers departing Melbourne have been told no Sydney flights are currently leaving the airport.
NSW school holidays begin today, meaning many families could be affected by the delays.
Passengers have been told the system fault is affecting flights around Australia.
News.com.au has contacted Airservices Australia, which is responsible for air traffic control around the country, for comment.
People who are scheduled to fly today are encouraged to check flight times with their airline.