Police swarmed through Richmond chasing suspects after a youth was stabbed on a train at the town's railway station on Wednesday.

But it was the heroic actions of two boat builders that helped catch one of the suspects.

At 11.40am police were called to Richmond Station to reports of a youth having been stabbed on a Waterloo to Reading service.

Several witnesses reported seeing a group of youths leaving the station shortly after the incident and police soon tracked one to Richmond riverside.

Luke Scott and Matt Arthur of Richmond Bridge Boat Hire saw a suspect sprinting across Richmond Bridge and jump onto the bank of the Twickenham side of the river and decided to help the police catch him.

Mr Scott explained: "We thought he was a jumper' before we realised he was being chased. We followed his footsteps from this side of the river and could see that he was going through the trees looking for a place to hide."

Uncertain of the situation they might find themselves in the pair took with them a large piece of wood.

Mr Scott added: "We went over in a rowing boat and spotted him. We said Hello mate' and pointed the police to where he was."

Richmond and Twickenham Times news editor Sarah Bell witnessed the incident as she walked over Richmond Bridge: "I saw about four police cars dive down Ducks Walk. As soon as I saw that many police in one place I knew something must be going on.

"I then saw the boys in the boat flush the youth out of a bush, he leapt over the fence and ran off chased by police. Many people had stopped to watch what was happening."

The suspect fled along the towpath, over Twickenham Bridge and into Old Deer Park where he once again hid in the bushes before he was sniffed out by a police dog and arrested by a member of the South Richmond Safer Neighbourhood Team.

Meanwhile the Reading-bound platform at Richmond Station was closed and the line shut for about an hour.

The London Ambulance Service attended the scene and an ambulance helicopter landed on Richmond Green delivering vital medical support to the victim, a 15-year-old male who had been stabbed several times in the lower chest.

He was taken to St George's Hospital in Tooting and on Thursday was reported to be in a stable condition.

The train on which the youths were travelling was sealed and taken to the depot for further inspection. Police dogs were deployed to Richmond station where they searched the track and surrounding area.

Six people have been arrested in relation to the incident, which is believed to have been gang-related.

It is believed the group boarded the train at Clapham Junction and no other passengers or train crew were injured.

A spokesman for British Transport Police, who are investigating the stabbing, said: "Investigations are continuing and police are appealing to any members of the public who were on the train or at or around the station at 11.40am to contact us as they may hold vital information."

Anyone with information is asked to contact the witness appeal line on 0207 391 5275 quoting background log B8 16/8/2006.