A schizophrenic convicted of stabbing a stranger more than 20 times has escaped from a mental hospital.

Police have warned the public not to approach Mark Ricketts, 38, who was held at the high security Broadmoor hospital in Berkshire home to criminals such as the "Yorkshire ripper".

Yesterday Ricketts was taken to visit Springfield hospital in Tooting, south London. At around 2.00pm, during his exercise on the grounds, he ran off towards the neighbouring Springfield Golf course and Burntwood Lane.

Scotland Yard said Ricketts needs daily medication, but does not have any pills with him. "This may cause him to act in a violent manner."

In 1994 Ricketts was convicted of launching a frenzied knife attack on doorman Mark Kemp, then 24. He dragged the man, a stranger to him, out of an amusement arcade into a Tube station, where he stabbed him repeatedly. Kemp barely survived. The Central Criminal Court sent Ricketts to Broadmoor indefinitely.

Nine months before the attack Ricketts was released from Springfield hospital, where he was kept after shattering house windows.

Ricketts was born in Birmingham but moved to Tooting at the age of three where he has spent most of his life, the Met said. He has family and friends in London.

A spokesman of Broadmoor said they launched in internal inquiry into how Ricketts managed to escape.

Police described Ricketts as a black man with brown eyes, a shaved head and face and short stubble all over. He is about 6'2" tall and has a stocky frame weighing about 108kg (17 stone). When he escaped, he was wearing blue jeans with a blue denim jacket, a long-sleeved blue shirt and white Reebok trainers. He walks with a "distinctive gait, long strides and bent forward".

Scotland Yard classed him as of "medium-risk". They urged people who see him to dial 999.