A man has been transferred to a specialist burns unit after a blaze at a flat in Corby.
A 38-year-old Polish man has been sent to Whiston Hospital, Merseyside, which has a specialist burns unit, after the fire broke out in Post Office Close, in the Old Village.
Police described his condition as “critical but stable”.
Smoke and flames were seen by neighbours during the incident at about 10.15am on Saturday.
Three other men were treated in hospital.
The first and second floors were damaged and the outside of the property was left blackened.
A police spokesman said: “We are aware of it, although essentially it has been a fire service investigation to date. The fire is still unexplained.
“There were four men in the property at the time of the fire. Three managed to exit of their own accord. One man was trapped in a bedroom in the property, a 38-year-old Polish national who was taken initially to Kettering General Hospital with significant burns.”
Ray Lilley, Corby councillor for the Old Village and chairman of its residents’ association, said: “The Old Village has very senior people and you don’t really come across stuff like this. People are very concerned but I don’t think they’re worried it will happen again.”
A neighbour, who asked not to be named, said she was first alerted to the blaze by firefighters banging on her door and had to escape with two young children.
She said: “I don’t really want to stay here to be honest.
“It has put me off the area.”
Corby Council said it helped the occupants of a property find temporary accommodation until a permanent solution is found. A Northamptonshire Fire and Rescue Service spokesman said the cause of the fire was still “under investigation”.