A 20-metre crane has collapsed on a cluster of properties in east London injuring four, as emergency workers search for one person who has not yet been rescued.
Crews have been battling to free those stuck in two terraced houses and a block of flats under construction on Compton Close, which were crushed by the crane.
A spokesman for the London Fire Brigade said rescue teams are still searching for one person, believed to be an adult.
The LFB is using a drone to provide aerial images to avoid the rescue operation.
A video posted online by a witness shows the top storey of the four-floor block of flats caved in with the crane lying on top of it.
A London Ambulance Service spokesperson said: "We were called at 2.42pm to reports of an incident involving a crane collapsing near Watts Grove, Bow.
“We dispatched a number of specialist resources including an advanced paramedic, ambulance crews and our hazardous area response team (HART), with the first of our medics arriving within three minutes.
“Currently our crews have treated four people at the scene. We treated two of these patients for head injuries and took them to hospital and we assessed the other two patients at the scene.
“We are working closely with other members of the emergency services at the scene with more updates to follow.”
BREAKING: A crane has collapsed on a house in Bow, east London.
London Fire Brigade says crews are working to free people trapped inside.
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Assistant commissioner Graham Ellis said: "Our urban search and rescue crews are undertaking a complex rescue operation and using specialist equipment to search the properties.
"This is a multi-agency response and is likely to be a protracted incident. I would ask people to avoid the area."
Basil Long, a 39-year-old housing lawyer, lives opposite the construction site where the crane came down.
"It was a real shock when I saw it fall," he said. "I had actually been in the bedroom at the time. There was a lot of shouting going on. I literally saw it topple over.
"It was terrifying. You could see the people in the tower trying to run down as fast as they could.
"After it came down, the site was evacuated and they got people out. I was evacuated at about 3.45pm. I'm still shaking."
National officer of the Unite union, Jerry Swain, said there must be "an urgent, full and complete investigation into the circumstances that led to this accident".
He added: "The preliminary findings of which must be released in weeks, rather than months or years, in order to ensure that similar accidents are avoided in the future."