The singer uploaded a clip on Tuesday showing highlights from the song's music video along with a message.

"Your support over the years has meant the absolute world to me," she wrote.

Streaming service Deezer says more than a quarter of her current fans weren't even born when the song was released in 1998.

Britney was just 16 when the song was released on 23 October 1998. It reached number one in at least 18 countries, including the UK.

She became a global superstar and went on to have hits including Toxic, Womanizer and Oops!...I Did It Again.

In the post, Britney said: "It's hard to put into words what today means to me… 20 years ago, the world heard my music for the very first time!

"So much has happened since then… but what I really want to say is thank you to my amazing fans who have been there for me since day one."

The 36-year-old has had some highs and lows over her 20-year career.

In 2007, she had a string of high-profile public spats, paparazzi run-ins and family feuds.

Britney is still touring

More recently she headlined Brighton Pride and played Scarborough. Next year she'll take up a new Las Vegas residency.

To mark 20 years since ...Baby One More Time, Deezer revealed her most-streamed song of 2018 was her 2004 hit Toxic.

Its data showed that 28% of people listening to her tracks this year were aged between 18 and 24 - so some of them wouldn't have been alive when she released her first single.