Three Londoners battled to save a smartly-dressed man who was fatally stabbed near a south London Tube station during this morning's rush hour, according to witnesses.

One passer-by desperately tried to save the man by performing CPR on him for five minutes before the emergency services arrived after the stabbing near Morden station just after 8am.

Another was on hand while a third made frantic phone calls, a witness said.

The man, said to be aged in his 20s, died at the scene.

The stab victim, said to have been dressed smartly in a trousers and shirt, was walking in Kendor Gardens - a leafy shortcut to the station used by rush hour commuters.

Megan Rayner, 62, whose house overlooks the park, said: "I looked out my window and saw three people standing in the park by a tree.

"One bent down and another one went and phoned. One of them was on the ground and started doing CPR.

About five minutes later three police cars suddenly zoomed in."

Others told of their shock at seeing the London Air Ambulance land in the park.

Police with sniffer dogs were combing the bushes this afternoon and a phone box on Dorset Road was also cordoned off.

Another man, who did not want to be named, said the victim had been dressed in trousers and a shirt.

He said he looked like "a normal person on his way to work."

Police have launched a murder investigation.

Officers appealed for rush hour commuters who may have witnessed the attack to contact them.

Detective Chief Inspector Dave Reid said: "The stabbing occurred during the rush hour period and there would have been a number of people in the vicinity making their way to the train station.

"I am appealing for anyone who may have seen the stabbing or the events leading up to the incident to get in contact with us."

The victim's next of kin have yet to be informed.

A man was arrested on suspicion of wasting police time and subsequently arrested on suspicion of murder. He is being held in custody at a south London police station.

Anyone with any information is asked to contact police on 101 or Crimestoppers anonymously on 0800 555 111.