The Duchess of Cambridge was the centre of attention as thousands watched members of the Royal Family attend church on the Queen's Sandringham estate.
Police estimated that 3,000 people gathered outside the church and royal-watchers said scenes were reminiscent of the "Diana days".
The Duchess is spending her first Christmas as part of the Royal Family following her marriage to Prince William, now the Duke of Cambridge, in April.
By 9.30am hundreds were waiting at the gates, with queues stretching back around 300 yards.The Duchess, with the Duke at her side, spent 20 minutes greeting well-wishers after leaving the service.
Veteran royal-watcher Mary Relph, 77, from Shouldham, near Sandringham, said the royals had been spending Christmas at Sandringham for the last two decades and queues have never been as long.
"I have never seen queues like this on Christmas Day before, I have never seen this amount of people here since Diana was alive. People obviously came to see Kate Middleton. And she was fantastic," Mrs Relph said.
Journalist Alison Croose said she had not seen such large Christmas Day crowds at Sandringham for years.
"I agree with Mary, I have not seen crowds like this since back into the Diana days," said Mrs Croose, a former royal correspondent with Norwich-based regional newspaper the Eastern Daily Press.
"It reminded me of the Diana years - when Diana introduced Prince William to the crowds when he was about seven or eight. It was touching. Diana used to have her hand on his back. Now you see William with his hand on Kate's back. It was really nice."