The Wolff 355B tower crane had been erected just the previous day to work on a social housing site in Bow, east London.
A woman was found on the first floor of one of the houses hit by the crane and confirmed dead at the scene.
London Fire Brigade assistant commissioner Graham Ellis said: "A 20-metre crane collapsed onto a block of flats under development and into two terraced houses on Compton Close.
"Our Urban Search & Rescue crews undertook a complex rescue operation and used specialist equipment to search the properties. Sadly one woman died at the scene. The London Ambulance Service have confirmed that two people were taken to hospital with head injuries and a further two were treated at the scene."
Photographs after the collapse show the base of the crane off the ground, the crane’s 22-metre mast folded over the development under construction and the tip of the luffing jib coming to rest on at least two of the houses in the neighbouring terrace.
The integrity of the cross frame is shown to be intact but one of the four foundation pads is not. This will be a focus of investigations.
The crane was being used by Swan Housing Association/NU Living on the construction of its Watts Grove development, the UK’s first mid-rise cross laminated timber (CLT) housing development made of prefabricated modular units. Work started on site in June 2018.
The crane is from the hire fleet of Wolffkran Ltd – fomerly HTC until it was taken over by the German/Swiss manufacturer for whom it is the UK dealer. Wolffkran said that two of the injured people were its employees. Both are in hospital, with one seriously injured and the other scheduled to be released today.
Wolffkran said: "The Wolffkran management and staff are deeply upset by this tragedy and express their deepest sympathy to the family of the woman that died in the incident. Our thoughts are with all those affected, our own staff, and their families, and we thank the rescue teams for their work on site. Employees of Wolffkran Ltd have been on site since yesterday supporting the responsible authorities in their investigations and preparations to remove the crane from the site."
It added: "The affected crane is a Wolff luffing jib crane of type Wolff 355 B, which is one of Wolffkran’s most tried and tested cranes, reliable in operation worldwide, and currently in operation on 18 sites across the UK. The crane on the construction site in Bow was only 10 years old and was fully erected on a 22-metre tower the day before the incident.
Swan Housing Association said: “Swan/NU living are saddened by an incident at our Watts Grove site today. Our thoughts are with those affected at this difficult time. We thank the emergency services & everyone for their dedicated response. Our staff are supporting this emergency and the investigation.”
Jerry Swain, national officer for construction at the Unite trades union, said: “Yet again we have seen a crane collapse on a construction site. Our thoughts are with those injured in this accident and we hope that no one has been seriously injured and that there has been no loss of life.
"Unite is in the process of contacting the company to discover more details about this accident. There must be an urgent, full and complete investigation into the circumstances that led to this accident. The preliminary findings of which must be released in weeks, rather months or years, in order to ensure that similar accidents are avoided in the future.”
Tower Hamlets mayor John Biggs said: “Our thoughts are with everyone affected. Priority is to ensure safety but need answers as to how this happened.”
On an earlier visit to the site, he had been impressed by the building system that was being used. “By embracing this modern method of building they will be able to deliver projects faster and with less disruption for our residents,” he said.