THERE is one time each year when Margie Rawlinson can't help but get a little emotional.

Even as she waited in the arrivals hall at Sydney Airport on Sunday morning, straining to catch a glimpse of her sister coming through the gates, her eyes started to water.

When her older sister, Janet Oag, finally arrived after more than 24 hours in transit from Heathrow Airport, the pair embraced in tears.

''Excited is an understatement,'' Ms Oag, 50, said of her annual trip home from ''cold, miserable'' London to spend Christmas on Bilgola Beach with her sister, parents and relatives.

Christmas Eve is set to be the busiest day of the year at Sydney Airport's international terminal, as family and friends fly in from all corners of the globe to be together at Christmas.

The number of security and kerbside staff will double on Monday to deal with more than 120,000 people moving through the domestic and international terminals.

The number of plane arrivals does not increase significantly but many airlines have used larger planes to carry bigger loads.

Qantas will run extra services from ports such as like Manila, Santiago and Auckland and will upgrade from 737 to 767 aircraft to ferry the huge spike in passengers from New Zealand.

Ms Rawlinson, 48, said she and Ms Oag, who has lived in London for 13 years, have always been close and try to spend every Christmas together, no matter where in the world.

''I say to my two daughters, you'll be like us one day,'' she said, as her teenage daughter Zoe rolled her eyes with a smile.

''We're just really close,'' Ms Oag said. ''It's beautiful to be home.''

Flight QF2 from London was also carrying some precious cargo for a Camden couple, Andrew and Heather White.

Mrs White's daughter, son-in-law and three young grandchildren burst through the arrivals gate at 7.35am for their first Australian Christmas together.

''We didn't tell the kids where they were going until they got to Heathrow Airport,'' Mr White said. ''They've never been to Australia so they've been going nuts. There's been a great build-up and a lot of excitement.''

The family had plans for a grand Christmas lunch - ''goose, turkey, the lot,'' Mr White said - and a tour around the city to take in kangaroos, koalas, caves and beaches.

To be together for Christmas was ''priceless'', said Mrs White's daughter, Virginia Tarbotton.

Sydney Airport's Christmas Eve

• 177 arriving and departing international flights
• 463 domestic flights
• 120,000 passengers arriving or departing
• 29,000 pieces of outgoing luggage