A 43-year-old woman and three boys, aged 15, eight and four, have been killed in a house fire in Brent, north-west London.
The emergency services were called to the blaze in Tillett Close, Stonebridge, at about 01:20 BST.
A 41-year-old man was arrested at the scene on suspicion of murder and remains in custody, the Met Police said.
A further two people were taken to hospital, the Met said. Their conditions have not been disclosed. Two terraced three-storey homes were involved in the fire, which was brought under control by about 03:25, the London Fire Brigade said.
Eight fire engines and about 60 firefighters from stations across Wembley, Park Royal and Willesden were sent out to tackle the blaze.
Supt Steve Allen, from the Met’s local policing team in north-west London, said: “This is an extremely tragic incident and our thoughts are with everyone involved… we continue to work alongside investigators from the London Fire Brigade to establish the cause of the fire.”
Emergency services will remain in Tillett Close throughout the day as inquiries continue, the Met added.
Leader of Brent Council Muhammed Butt said in a statement: “Our deepest condolences, thoughts and prayers are with the families and friends of those who lost their lives in this horrific incident.
“The council has set up a rest centre nearby and a dedicated team has been looking after families who needed to be evacuated. We will continue to support those affected.
“We are working closely with the London Fire Brigade and the Metropolitan Police as they conduct their investigations into the cause of the fire, and will continue to offer them our full support and assistance.”
Dawn Butler, MP for Brent East, posted on X that she was “devastated to see the fatal fire” and her prayers were with the family and friends affected.
