A HOUSE fire which killed a woman and critically injured her five-year-old grandson was unlikely to have been caused deliberately, according to police.

Two other people, including the mother of the boy, managed to escape from the house in Thornaby, near Stockton, and were in hospital yesterday.

Neighbours have described the 40-year-old woman as a "beautiful, caring grandmother" and the boy as "a normal, healthy little boy who loved to play".

The child was in the burns unit of Newcastle General hospital last night after sustaining 90 per cent burns across his body. Police said his condition was very critical.

His grandmother was pronounced dead at the house in Havelock Street.

Firefighters fought through the flames to save the boy after being called at about 5pm on Tuesday.

The boy's 22-year-old mother and a 47-year-old man jumped from an upstairs window to escape. Both were being treated at the James Cook University Hospital for burns and smoke inhalation yesterday.

Police and Cleveland Fire Brigade have launched a joint investigation, but police said early indications showed it was unlikely the fire was started deliberately.

The street was cordoned off all day while forensic officers carried out their investigation.

Neighbour Maureen Hunter said: "The little one was a normal, healthy boy.

"We would be out playing on the street with all the others.

"This whole thing is just a terrible tragedy.

"Everyone here is just shocked. You just can't believe it."

Other neighbours described hearing shouting and the sound of windows smashing on the street as flames burst out of the terraced house.

Firefighters from Thornaby and Stockton battled intense heat and flames to tackle the fire.

"We did well just to get in the house at all and very well to recover people from inside," said Barry Waller, Thornaby Fire Station manager.

Speaking at the scene of the fire, Detective Inspector Paul Beddow said officers were still contacting members of the family last night and were hoping to talk to the survivors.

The coroner's officer has been informed.