To have this loss of life is absolutely tragic, our thoughts and prayers are with the family

Assistant divisional fire officer Alan Gill

The fire happened at 0200 BST in Charlbury Road, in the Pallister Park area of Middlesbrough while the children's parents, both in their 20s, were out.

Their mother, Marie Scully, was at work and their father, Robert Sands, was visiting his father.

Divisional officer Dave Bennett said firefighters arrived at the house four minutes after the emergency call was received.

He said: "We understand the babysitters were alerted to a loud noise upstairs and on checking they were confronted by thick black smoke."

The upstairs of the house was full of smoke

They left the house to raise the alarm.

Neighbour Simon Mallory ran into the house to try to rescue the children, who were in an upstairs bedroom, but the smoke was too thick.

Police and fire investigators were trying to establish the cause of the fire which is not being treated as suspicious.

Tests by forensice scientists and Cleveland Police's arson investigation unit have ruled out an electrical fault or gas explosion.

Smoke alarms were fitted both upstairs and downstairs in the home, a fire brigade spokesman said.

Tests were being carried out to see if they were working.

'Absolutely tragic'

Assistant divisional fire officer Alan Gill said: "There was no visibility, the smoke was that dense.

"To have this loss of life is absolutely tragic, our thoughts and prayers are with the family."

Distraught neighbours have placed floral tributes along a hedge outside the terraced house.