Horrified families awoke to find a bloodbath in their quiet apartment block after a stabbing which left a tenant seriously injured.

Parents taking young children to school were forced to "walk through blood" when they were confronted with the gruesome scene and found their flats in Thornton Heath cordoned off by police on Thursday morning.

A 26-year-old man was treated at St George's Hospital in Tooting for a serious stab wound to the arm that is thought to have severed his artery.

The victim left a trail of blood along the stairs, corridors and handrails of Redwood House in Thornton Road, as well as in the street as he fled to hospital, where he remains in a stable condition.

David Law-Kwang, 44, who has lived in the building for eight years, initially thought someone had been killed.

He said: "I was getting ready to take my dog for a walk and saw the police had locked down Fairlands Avenue at both ends. Then we found out there was a stabbing on the first floor. 

"There was so much blood we thought there had been a murder. Whoever stabbed the other person hit a main artery and there was arterial bleeding everywhere."

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Tenants said the block of flats was usually quiet

He added: "Everyone was shocked. There were people taking their kids to school in the morning who had to walk through the blood. It was pretty traumatic for everybody in the block."

Five of the 14 flats are thought to be occupied by families with children. 

One mother, with has a seven-month-year-old daughter and did not want to be named, said: "It was very distressing. We didn't leave our flat all day."

Nearby shops in Thornton Road were forced to close for the morning while police investigated the stabbing and Croydon Council contractors cleaned blood off the streets.

Mr Law-Kwang, who runs a recruitment company and described the flats as "usually pretty quiet", added: "I had to get in touch with the management of the building to come do a deep clean because there was blood all over the lobby as well."

A Metropolitan Police spokesman said the force was initially called to St George's Hospital 4.35am on Thursday to reports of a man being stabbed.

Officers then learned the attack had taken place at Redwood House and cordoned off the building for forensic examination. 

Two men are understood to live in the flat where the stabbing happened.

No arrests have been made. Police are continuing to investigate.