Two people have been discharged from hospital and a barber shop remains taped off after shocked residents saw a "man on fire" lying in the road.
Police, firefighters, paramedics and the Great North Air Ambulance Service (GNASS) were called to Stamfordham Road in Westerhope, Newcastle, on Tuesday morning.
Four people, two of which were suffering from serious injuries, were transported to the Royal Victoria Infirmary (RVI) in the city.
Read more: Investigation launched after man found with 'fatal injuries' on Northumberland street
Two people were discharged on Tuesday. The other two patients remain in hospital.
People in the area told Chronicle Live how they heard shouting and saw a "man on fire" lying in the road.
One person said how they had witnessed a passing lorry driver jump out of their vehicle and use a fire extinguisher on a person lying in the road.
They said: "The lorry driver was the first one there trying to help. He'd grabbed a fire extinguisher from the lorry and was trying to help a man who was on fire in the road. Lots of people quickly came to help."
Another resident said: "We heard screaming and footsteps and saw a man lying in the road. There was people trying to help."
On Wednesday morning, a police cordon remained around Amed's barber shop on Stamfordham Road. A police van was parked up at the scene and items had been left on the ground outside.
Northumbria Police is currently treating the incident as arson.
A spokesperson said the force was alerted to a report of a fire at a premises on Stamfordham Road in Newcastle at 10.05am.
They said: "Officers and emergency services attended the scene and four people were taken to hospital.
"Two people were discharged yesterday, while two remain in hospital for treatment.
"An investigation into the cause of the fire was launched and at this time officers are treating it as suspected arson.
"The fire has since been extinguished but a cordon remains in place and additional officers remain in the area, carrying out door-to -door enquiries and offering reassurance to residents.
"Enquiries are on-going into the incident and anyone with any CCTV footage or information is asked to dial 101 or report via our website’s ‘Tell us Something’ function, quoting log NP-20230523-0301."
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