Three children and one adult have died following a house fire in Brent, north-west London, the Metropolitan Police confirmed.
Police were called to assist the London Fire Brigade at Tillet Close in Stonebridge at 1.22am.
The three boys, aged 15, eight and four and a 43-year-old woman died in the early hours of Saturday morning.
A further two people, a woman in her 70s and a teenager, have been taken to hospital by the London Ambulance Service, with their condition currently unknown.
The fire occurred in the early hours of Saturday morning
PA
Their next-of-kin have been informed, the Met Police added.
A 41-year-old man was arrested at the scene in connection with the incident and remains in custody.
Superintendent 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.
"Officers arrested a man at the scene, and we continue to work alongside investigators from the London Fire Brigade to establish the cause of the fire.
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"Emergency services will remain in Tillett Close throughout the day as these inquiries take place."
Eight fire engines and around 70 firefighters from Wembley, Park Royal, Willesden and surrounding fire stations were deployed to the scenes, following over 20 calls reporting the fire.
Crews had the fire under control in just over two hours at 3.24am.
Four people left the properties before the Brigade arrived. All were assessed on scene by the London Ambulance Service, and two were taken to hospital for further treatment.
Around 70 firefighters attended the scene
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Assistant Commissioner Keeley Foster said: "This is an extremely tragic incident, and the thoughts of everyone across the Brigade are with those impacted by this incident.
"Upon arrival, firefighters were met with a well-developed fire, involving two adjoining properties. Crews immediately set to work carrying out firefighting operations in order to bring the incident under control.
"Sadly, a woman and three children have died as a result of this fire. Crews wearing breathing apparatus were able to rescue the woman and one of the children from the second floor, but they were later declared deceased at the scene. A further two children were discovered to have died in the fire, as crews carried out a search of the properties involved.
"Our specialist Fire Investigation Unit are working closely with colleagues from the Metropolitan Police Service to now determine the cause of this fire. We are working closely with our partners to support the community at this very sad time."
The Met Police have appealed to anyone with information to call 101 quoting CAD509/24May or anonymously through Crimestoppers online or by calling 0800 555 111.
