X Factor winner Alexandra Burke's single is selling so fast online she may reach the Christmas No 1 slot before the CD hits the stores.

HMV today said the 20-year-old singer's debut single is its fastest ever selling download — and bookmakers predicted she could sell a million copies in a week.

Winner: Alexandra's single is proving popular

Burke, from Islington, won the TV final on Saturday night and a recording contract worth £1 million.

Her version of Leonard Cohen's Hallelujah was released online hours later, priced 69p on HMV.

Gennaro Castaldo from HMV said: “Hallelujah promises to be the biggest X Factor release yet, and the chances are that Alexandra will have the Christmas No 1 single in the bag even before her CD single officially hits the stores midweek.”

Burke today begins an unprecedented whirlwind promotional tour of interviews, public appearances and TV shows.

Record label Sony BMG will put her through a media “blitz” as she plugs the new single, and she is set to make TV appearances on GMTV, The One Show, This Morning and Richard and Judy's New Position.

A staggering 14.6 million viewers —58 per cent of the total TV audience —tuned in for the final, in which Burke triumphed over boy band JLS and Northern Irish teenager Eoghan Quigg.

More than eight million viewers voted in what bookmakers described as the biggest reality television betting event they had witnessed. Burke's chances of topping the charts this week were rated as 1/8 by Ladbrokes, and 1/5 by Hill.

A William Hill spokesman said: “The winning song could do the unthinkable and sell a million copies in a week.”

Ladbrokes spokesman Nick Weinberg said: “It's as close to a certainty as you're likely to find.”

Burke said on GMTV today that she plans to recreate her duet with Beyoncé. She said it had been a “dream come true” to perform her heroine's hit Listen with her in the final. She would also like to sing with 2006 X Factor winner Leona Lewis, from Hackney.

“I would love to do a duet with Leona, to show the world how different we are,” she said.

Her next major live appearance will be at the O2 arena on New Year's Eve, where she will perform alongside Sir Elton John.

The former pub singer will also perform at venues across the country as part of the show's lucrative spin-off tour.

Industry sources say the show's impresario, Simon Cowell, is planning to remove Burke from the spotlight for a few months and send her to Los Angeles to work on a debut album in the hope that she can emulate the success of Lewis.

Cowell said: “No one can deny what this girl has achieved. There would have been a riot if she hadn't won. I've got a really good feeling this is going to be one of the biggest-selling X Factor singles. I've got a good feeling about her.”

Burke dedicated her performance to her mother Melissa Bell, the former Soul II Soul singer, who has kidney dialysis three times a week as she suffers from chronic diabetes.