A woman and three young children have died and two other people are in hospital after a house fire, emergency services have said.
Essex Police confirmed that three children and a woman had died in the blaze at Barn Mead in Harlow, Essex, and that two people were in hospital, one of them in a critical condition.
A police statement said: "The cause of the fire is under investigation and detectives are looking at the circumstances leading up to the fire, and ask that anyone who was in the area of Barn Mead in the early hours of Monday and has any information contacts police at Harlow police station on 101."
Firefighters called to the scene described the house as being "100% well alight", with flames coming from the front and back doors.
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 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."
There is a burnt-out car yards from the house which is believed to have caught light at the same time as the house fire. It is not known if the two incidents were linked but firefighters were seen examining the vehicle.
It is understood the family who lived at the address were of Asian origin.