A mother and her three children have been killed in a house fire in Brent, north-west London.
The emergency services were called at about 01:20 BST to the blaze in Tillett Close, Stonebridge, where they found the victims - a 43-year-old woman, a 15-year-old girl and two boys aged eight and four.
A 41-year-old man was arrested at the scene on suspicion of murder and remains in custody, the Met Police said.
Another woman in her 70s and a teenage girl were also taken to hospital, the Met said. Their conditions have not been disclosed.
'Extremely tragic incident'
The Met Police had initially said three boys had been killed in the fire but have since updated that information.
In a statement on Saturday afternoon, Supt Steve Allen confirmed the woman who died was confirmed as the mother of the three children.
Two terraced three-storey homes were involved in the fire, which was brought under control by about 03:25, the London Fire Brigade (LFB) said.
Eight fire engines and about 70 firefighters from stations across Wembley, Park Royal and Willesden were sent out to tackle the blaze, which was reported by neighbours.
One woman, who said the family had moved to the UK from Pakistan more than 20 years ago, told the BBC she heard a crashing sound then went out to find the building next door was on fire.
Mohamed Labidi, a 38-year-old teacher who lives on Tillett Close, said he "can't even look at the house right now".
Speaking to the PA news agency, he said he knew the woman who died, and that the family were "really good people".
"We used to socialise together," he said.
Another neighbour Cecilia Marquis, 60, said she was "stunned by the devastation" of the blaze.
"This will leave a devastating impact. I just feel numb," she added.
Another neighbour, who did not wish to be named, said: "It's a very distressing time for us and the neighbourhood.
"We've all grown up together. We've all lived in these houses for 25, 30 years. Everyone knows everyone.
"It was a very big fire. The fire was blazing. It was non-stop.
"It's a very tragic time."
In a statement, the LFB said: "A woman and a child were rescued from the second floor of one property by crews wearing breathing apparatus and received immediate emergency care.
"Both were sadly declared deceased at the scene by a Helicopter Emergency Services (HEMS) team.
"Two more children were discovered inside the property as crews carried out firefighting operations and were declared deceased at the scene."
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."
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."
Mayor of London Sir Sadiq Khan posted on X: "This is devastating news and my thoughts are with the family, friends and wider community of the four people who sadly have lost their lives."
Assistant commissioner of the LFB Keeley Foster said the thoughts of everyone across the brigade were with those affected by the fire, adding that the service was working with police to determine the cause of the fire.
Emergency services will remain in Tillett Close throughout the day as inquiries continue.
