LONDON ? A schizophrenic man admitted Monday punching British singer Leona Lewis in the face during a book signing, an attack which left the pop star "completely devastated".

Peter Kowalczyk, 29, from Waterloo in south London, pleaded guilty at City of Westminster Magistrates' Court to common assault and was detained under the Mental Health Act.

He was heard to say "gotcha (got you)" as he hit the singer on October 14 in a book store in central London.

Prosecutor Melanie Lee said Lewis, 24, was left with whiplash symptoms, redness and swelling to the face after Kowalczyk punched her with his right fist as she went to sign his copy of her autobiography.

"I feel completely devastated by this attack," Lewis said in a statement read out by Lee.

"Now I am very frightened about going out in public and I don't know where the next attack will come from and if this will be more serious than what has just happened," said the singer.

District Judge Howard Riddle ordered Kowalczyk to remain in hospital for an indeterminate period.

"This is what happens when you don't take your medication. A woman is now devastated," he said.

Kowalczyk was led from the court by medical staff.

Lewis was catapulted to fame by winning a television talent show in 2006. In 2008, she became the first British woman to top the US charts for over 20 years with her single "Bleeding Love."