Dozens of people have been evacuated from their homes after a crane collapsed on houses in east London killing one woman and injuring others.
The 20-metre crane fell on a site where flats were being constructed, and crashed into two terraced houses in Compton Close, Bow, on Wednesday afternoon.
It is understood the crane was still in the process of being erected when it collapsed.
Mayor of Tower Hamlets John Biggs said around 40 people were asked to leave their homes, but added that as people returned from work the number of residents affected could have increased.
He added it was unknown when they could return home as the site has to be made safe.
A large part of the roof could be seen to be completely caved in on one of the houses.
London Fire Brigade (LFB) said a woman was found on the first floor of one of the houses hit by the crane and confirmed dead at the scene.
Four people were treated by the London Ambulance Service, with two of them treated for head injuries and taken to hospital.
The crane that collapsed was being used by Swan Housing Association and NU living, and appeared to be a Wolff crane.
A spokeswoman for Swan Housing Association and NU living said they are "deeply saddened by an incident that has occurred at our Watts Grove development site this afternoon", adding: "Our staff are on site to provide support to the emergency response and the investigation."
Work on the Watts Grove site began in 2018 where the one, two and three-bed shared ownership apartments are replacing an electrical substation building, according to the NU living website.
A spokeswoman for Tower Hamlets said a rest centre has been set up to help people who are displaced and accommodation is being provided to those who need it.
Speaking about the crane, Mr Biggs told the PA news agency: "It was still being erected as I understand it."
He added: "Someone else told me it was being erected today, so it's in the last 48 hours it's been going up.
"So I guess it might have started yesterday and carried on today. Sometimes they seem to take a couple of days to go up."
Mr Biggs said the incident will worry people and pointed out the importance of learning from what happened.
"We have more construction in my part of London than just about anywhere else in the country, and it's important that we get on top of it of course, and learn any lessons, see were there any errors.
"A lot of people will be worried by this and I guess there's a question of public assurance as well," he said.
Asked how long people will be out of their homes, he said: "No idea whatsoever. Obviously you need to make sure the site is safe."
Mr Biggs said there is a possibility that utilities and supplies of water and electricity may be affected by the damage.
He said structural engineering assessments will need to be carried out to check whether structures are safe, and said that "ideally" people will be back in their homes on Thursday, but that it may be "a few days yet".
Meanwhile, Unite national officer 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."