Seven people were rescued after a mezzanine floor collapsed at an east London bar.
The incident happened at Two More Years in Roach Road, Hackney Wick, at 4.44pm on Saturday.
London Ambulance Service (LAS) declared a major incident after emergency services were called to reports that part of a building had collapsed.
Crews treated 13 people, with three having potentially serious injuries and 10 having minor injuries. Four of the injured were taken to hospitals and major trauma centres.
LAS strategic commander Brian Jordan said: “We declared a major incident and dispatched a number of resources to the scene.
“This included incident response officers, advanced paramedics, tactical advisers, clinical team managers, units from our hazardous area response team and several ambulances and fast response unit car crews.
“We also dispatched teams from London’s Air Ambulance. We worked closely with emergency services partners and treated 13 people.
“Three patients had potentially serious injuries and 10 had more minor injuries. We took four people to hospitals and major trauma centres.”
A man who was in the venue at the time said: “There was just this sort of cracking sort of noise and dust started coming down.
“Me and my friend just ran to the side and the whole thing just came down in a matter of seconds.”
The man said he saw one person being brought out on a stretcher and put into an ambulance, but he said most of the injured appeared to have cuts and bruises rather than anything serious.
LFB station commander Sacha Clement, who was at the scene, said: “Firefighters carried out a systematic search of the building and rescued seven people from inside.
“They were trapped on the remaining part of the mezzanine floor and crews used a ladder to bridge between the floor and the internal staircase to get them safely out of the building.
“We are working with our emergency services partners, and a number of people have been treated at the scene and taken to hospital.”
LFB added around 50 people left the building before crews arrived.
Rushanara Ali, Labour MP for Bethnal Green and Bow, tweeted: “Very concerned about the collapse of part of a building at Roach Road #fishisland.
“My thoughts are with all those affected and their loved ones. Grateful to London Ambulance and TowerHamletsNow emergency response services for their support at this time.”
The Metropolitan Police said it was called by the LAS at 4.47pm to reports of a partial building collapse at a pub, although a police cordon has since been lifted.