Leona Lewis has been attacked at a book signing in London, it's been reported.

The incident is said to have taken place at Waterstones book store at Piccadilly as the former X Factor star signed copies of her autobiography Dreams.

Leona arriving at Waterstones Piccadilly on Wednesday (Splash News)

Police were called to the store, which is still open, according to the BBC.

A spokesman for Scotland Yard told Sky News: "We were called to Waterstones Piccadilly Circus at 4:35pm to reports of an assault.

"It appears that a male has slapped a female at the location."

The X Factor winner signing copies of her autobiography before the attack (WENN.com)

Leona was later seen crying as she left the store.

A spokesperson and witness to the attack said: "She was doing a signing to launch her new book. Hundreds of fans had been queuing since last night.

"A guy came up and punched her to the side of the head. She is absolutely gutted she did not get the signings finished."

Dreams, the 24-year-old's first book, includes dialogue about the singer's life, as well as 100 new photographs taken by Dean Freeman.

Lewis's debut album 'Spirit' has sold nearly five million copies around the world since it was released in 2007.