Extended trading hours and disruptions to payments and services will take place across Sydney this Christmas and New Year.

All service centres and most phone lines providing Centrelink, Medicare and Child Support services will be closed from December 26-28 and on Monday, January 2 , while self-service options will continue to be available during the holiday period.

Payments made to child support after December 22 may be slowed by the holidays. While most other payments will not be delayed, some may arrive earlier than usual.

"The department's Express Plus mobile apps, phone self-service lines and online accounts through myGov, are the easiest way to do your business with us over the Christmas and New Year break," said Department of Human Services general manager Hank Jongen.