Cindy Crawford to retire from modelling on 50th birthday?

The 49-year-old, who turns 50 on February 20, told United Airlines' Rhapsody magazine she thought it was time to "move on" from modelling.

Promoting her new book, Becoming By Cindy Crawford, the supermodel said the writing process had assisted her to "maybe not say goodbye … but move on" from the profession she has been in since she was a teenager.

"I'm sure I'll have my picture taken for 10 more years, but not as a model any more," Crawford said.

"And that's OK. I've done it. I've worked with all these incredible photographers. What else do I need to do? I can't keep reinventing myself. I shouldn't have to keep proving myself. I don't want to."

Becoming By Cindy Crawford (which has been published by Rizzoli New York, the same publishers behind Kim Kardashian's Selfish photo book), chronicles Crawford's career.

The Illinois native started modelling aged 17 after dropping out of chemical engineering at Northwestern University, where she was studying on an academic scholarship.

She went on to become one of the world's most recognisable names and faces, appearing on the covers of Vogue, Harper's Bazaar and Cosmopolitan, and walking runways for Chanel, Valentino, Christian Dior and Michael Kors.

In 1995, Forbes magazine named Crawford the highest paid model on the planet.

In 2000, she quit modelling full time, instead only appearing occasionally in fashion magazines and campaigns.

In recent years, alongside occasional magazine covers, Crawford has released a number of homewares lines, and has become a spokesperson for child cancer charities, including the Ronald McDonald House.

As Crawford steps away from the spotlight it seems her 14-year-old daughter Kaia Gerber (one of Crawford's two children with husband Rande Gerber) is ready to take her place.

Kaia, who has 339,000 Instagram followers, is a spitting image of her mother and already has a contract with IMG.

Speaking to Teen Vogue in December, she said that she realised she wanted to follow in her mother's footsteps at a very young age.

"After shooting a Young Versace ad when I was 10 years old, all I could think was, this is it," she said.