The discovery of the bodies of a 26-year-old woman and her two daughters is being treated as murder.
The identities of the dead have not yet been revealed
The bodies were found in East Ham, east London, on Wednesday morning after a family member became concerned about the mother's welfare.
Police forced their way into the terraced house in Nelson Street and found the woman and her daughters, aged five and six, in the bedroom.
The bodies have been removed and post-mortem tests will be carried out.
Officers have confirmed there were no signs of forced entry.
The identities of the dead have not been revealed. Their relatives are being informed, police said.
It is understood police did not find anything at the scene that gave any immediate indication how the woman and children had died.
Chand Kaushal, a shopkeeper whose store is around the corner from the house, said: "It is shocking. I do know people who live along that street but I've not seen anyone coming and going from that particular house."
A neighbour said the dead woman's sister visited him on Tuesday after failing to hear from her for nine days.
The pair of them got no response at the house and were struck by how cold it was, so decided to contact the police.
Another neighbour who lived along the same street described the woman living at the house as "very pleasant but quiet".
The street has been cordoned off and only residents were being allowed to pass.