Private security guards were today posted outside an exclusive private school after a man stabbed by moped thugs collapsed on its front steps.

The smartly dressed victim staggered into the doorway of £20,000-a-year Knightsbridge School as parents were picking their children up at about 4pm last night.

Staff attempted to stop the bleeding before the victim, who is in his twenties, was taken to hospital. His condition was not life-threatening.

Police said the attack was the first of four linked muggings in just two hours in the wealthy central London neighbourhood yesterday.

The muggers attempted to rob another victim in Bryanston Square 45 minutes later, before targeting a woman in Elm Park Gardens at 5.50pm. Seconds later, two men on a moped targeted another victim in Onslow Gardens.

This morning, two bodyguards were posted near the school campus in Lennox Gardens and Pont Street. The extra security were said to have been provided by a wealthy family to ensure a safe passage for their children.

Magoo Giles, principal of the 430-pupil school which opened in 2005 for children ages three to 13, told the Standard: “The victim was, as far as I know, approached by two people on a moped in helmets who stabbed him when he wouldn’t hand over his watch.

“He got to the school where our staff offered him first aid and tried to stop the bleeding. I am very proud of the way they acted. The man was speaking but was in shock.

“He was taken to hospital but I understand he has since been discharged. The school has a counselling service for anyone who needs it after witnessing an incident like this.

“Our parents have been very supportive and with the nights drawing in we all need to be extra vigilant.”

The victim, who has no connection with the school, was said to have had a knife wound to his buttocks.

A female witness said: “There were two guys on a bike. They were kicking and hitting the man. One made a slash motion but I didn’t see the knife.

“It looked like the smartly dressed man was trying to fight them off. They were shouting at him to give them something. It was very vicious.”

Rawan Halabi Majali, whose children attend the school, said: “This happened when the kids were leaving school. What a horrible and traumatic event for kids to experience.”

One of the guards said today: “There is usually one of us but today the family wanted two after the attack… these robbers have machetes and long knives. It’s tough when you are not armed.”

Comedian Michael McIntyre was robbed of a £15,000 watch by two hammer-wielding men on mopeds outside his children’s school in Golders Green last year.