Four children have died and a mother and child are in a critical condition after a fire in Harlow.
Essex County Fire and Rescue Service said fire crews were called to Barn Mead at 1.45am on Monday , where they found a house "well alight" with flames pouring from the building.
Firefighters rescued five people from the building, but a spokeswoman for the service said that four children died.
Assistant divisional officer Steve Foster, incident commander, said: "Crews arriving at the scene did everything they could. They were faced with a rapidly developed fire and went straight into the burning building wearing breathing apparatus to bring people out as quickly as possible. Once casualties were out, they worked alongside ambulance teams to do all they could.
"Fire investigation teams are now working with police to establish how this tragedy happened and our thoughts are with those the family left behind."
A spokeswoman for the service said the father was not at home when the blaze broke out, and that the four fatalities occurred at the scene.
She said: "We understand that firefighters brought them out of the house and were doing CPR (cardiopulmonary resuscitation) outside, and that they were confirmed dead at the scene.
"The incident is now in the hands of Essex Police."
A joint police and fire service investigation will be carried out to establish the cause of the fire.