The track, called This Is It, is the first to emerge since the star died in June, and features backing vocals by Jackson's brothers.

It has been released on the singer's website and to radio stations and will be the only original song on a double CD due to be released soon.

At the time of its airing there was also no information about when the song was written and recorded, who else worked on it and whether his brothers had recorded their vocals before or after he died.

It went out on his website, michaeljackson.com, at 0400GMT this morning.

It is likely to be the first of many new songs to see the light of day, including ones that could feature Akon and Will.i.am, who Jackson was working with before his death.

Jackson's official website described it as a "brand new single", which would be "released" on 12 October.

But a spokesperson said the term "released" referred to its distribution to radio stations and other media outlets.

The song takes its name from the series of comeback shows that Jackson was due to perform at London's O2 arena this summer and early next year.