Australia Post says any Christmas gifts that are not posted on Monday will have to be sent by express post, with the deadline for that December 20 - or December 15 for WA and the NT.

Australia Post's Rod Barnes says the corporation is expected to exceed last December's delivery record of more than 52 million parcels, with more than three million a day to reach customers on the busiest days.

"We know a lot of people did get their Christmas shopping done early during those big cyber sales and as a result we've been delivering over 2.3 million parcels each weekday," he said on Monday.

"But for those who haven't had the chance to finalise their gifts yet, we're doing everything we can to give them the best chance of arriving, including delivering on weekends and until early evening where needed, up until Christmas Eve."

To give people as much time as possible to send gifts, more than 380 Post Offices have extended trading hours across the country.

Australian Associated Press