Windy weather has forced the cancellation of up to 25 domestic flights out of Sydney Airport on Monday morning, while a severe weather warning has been issued for damaging winds that are expected to worsen into the afternoon.

Sydney Airport had to reduce its operation to a single runway about 8am on Monday, resulting in up to 25 cancelled flights and delays averaging between 30 minutes and one hour.

No international flights have been cancelled, and two runways are now back in operation, a spokesman for the airport said.

However, the Bureau of Meteorology has issued severe weather warning for damaging winds affecting much of the NSW coast over the course of Monday afternoon and evening.