A retired Auckland man, who came forward today to claim a Christmas lottery prize worth almost $13 million, kept his ticket in his blood pressure monitor because it made his heart go "nuts".

The winning Lotto Powerball ticket, worth $12,991,369, was bought at Magascene in Takapuna on Auckland's North Shore.

The man, who wishes to remain anonymous, bought the ticket because he was "feeling lucky" after winning a small sports bet with friends.

"I was feeling lucky after my small win, so decided to try for a big win," the man said.

The man found out he was a winner after reading the paper on Boxing Day and celebrated by having a spontaneous champagne breakfast with family .

"I just felt numb, and then felt my heart racing, it was hard to believe that I had the winning ticket in my wallet," he said.

Before travelling to Wellington to claim his winnings the man hid his ticket in his blood pressure monitor.

"I figured that the ticket kept making my heart go nuts, so it was an appropriate place to keep it."

The man plans to pay off the last of his mortgage and help out close family with his win.

"I also want to invest in some good New Zealand businesses and help out some charities - especially those that help grow and support our emerging athletes," he said.

"There is a Ferrari dealership not far from the Lotteries office, so I might go and visit them today," he joked.