A young man is fighting for his life and three others were also injured after a knife attack outside a train station.
The 23-year-old man left critically injured was one of four people taken to hospital after the attack outside Harrow-on-the-Hill in the early hours of Sunday.
One man was left “drenched in blood” while another “shouted in pure agony", a witness said.
Will Njobvu had just got off a night bus at about 3.45am when he heard screaming.
He said: “I saw two people on the floor and one was drenched in blood while the other was a few metres away on the floor shouting in pure agony.
“The ambulance came a few minutes after and started treating the victims. I spoke to someone on the ground who saw the incident unfold - he told me they were stabbed by a group of youths after a fight broke out.
“There was also another guy walking around with his top off and blood on his hands.
“That's all I saw but it was quite distressing - I've never seen that much blood in my life.”
Police and paramedics rushed to the scene in Station Road and all four victims were taken to hospital.
A 19-year-old is described as being in a serious but stable condition, while a 20-year-old and and a 21-year-old, who also suffered stab injuries, have been discharged from hospital.
A Met Police spokesman added: “Detectives from Harrow CID are investigating. Enquiries are taking place to establish the full circumstances of the incident.
“There has been no arrest at this early stage.”
Road closures were put in place as forensics officers carried out an investigation.
It is the second stabbing in the area in the space of the week, after a man was rushed to hospital after he was stabbed multiple times in Harrow town centre.
Anyone who witnessed the incident, or has information that may assist police, should call Harrow CID via 101 or Crimestoppers on 0800 555 111.
