Airservices Australia said air traffic controllers closed the airport's parallel north-south runways because of strong westerly winds.

All aircraft - which are prohibited from landing in strong cross winds - will be forced to use the east-west runways.

Air traffic controllers have also reduced the number of aircraft movements per hour to match the "operating conditions".

In a statement, Airservices Australia said delays of up to one hour are expected.

"The winds are forecast to continue throughout the afternoon and overnight, increasing in strength tomorrow," the statement said.

"All parts of the aviation industry are working together to minimise delays for travellers."

The delays experienced in Sydney are expected to flow-on to services operating out of Melbourne and Sydney.

International and domestic flights are currently on, or close to, schedule but an Airservices Australia spokesman said the impact will be noticed once the afternoon peak begins.

"If we are using both parallel runways then we can average about 50 movements an hour, but when we are using a single runway only we can expect to operate at only 25," he said.

"Now 25 movements during the lunchtime period isn't a big problem ... but it will start to be a problem once we reach the afternoon peak."

The spokesman said anyone heading to the airport should first contact their airline.

He also warned that restricted operations and delays are expected to continue tomorrow.