hree people were rushed to hospital after a section of the stand for spectators watching the Trooping the Colour ceremony collapsed on Saturday.
Two others were treated at the scene by paramedics following the incident in Horse Guards Road at around 11am.
Part of the stand was evacuated after the incident, while pictures showed a woman being taken away on a stretcher by paramedics from St John’s Ambulance.
The ceremony, which involves a parade by the Household Division and Horse Guards, was cut short after emergency services arrived at the scene.
A large crowd had gathered at the event, which is the Major General’s review of the parade ahead of the full event on June 2 for the Queen’s Jubilee celebrations.
Zoe Clark-Coates, a TV presenter and author who was among the crowd, wrote on Twitter: “What we just witnessed was terrifying, but we are safe!
“Part of the floor in the stand collapsed, and at least one person fell through. We are praying for the injured and shocked. The stands are being evacuated.”
A London Ambulance Service spokesman said: “We worked alongside St John Ambulance volunteers to treat five people at the scene.
“We took one patient to a major trauma centre as a priority. St John Ambulance took a second patient to a major trauma centre as a priority. We discharged three patients at the scene.”
They added that transport was later arranged for a third person to go to hospital.
Another witness told the Mirror they had heard a scream after the stand collapsed.
“The paramedics rushed in but started yelling ‘we can’t find her’,” they said.
“She was extracted after several minutes and seemed fine but badly shaken and was put on a stretcher and loaded into an ambulance.
“The crowd was calm but was later moved out of that section. Then a second section had a similar collapse and the crowd was moved but with no one falling through.”
The Ministry of Defence confirmed that sections of the spectator stands collapsed on Saturday morning.
An Army spokesman said: “During the Major General’s Review on Horse Guards Parade, two parts of the viewing stand unfortunately gave way, resulting in a small number of injuries.
“The emergency services were called to assist those who were injured and the remaining crowds were safely evacuated from the stands.
“Safety is our number one priority and we are urgently working with our partners and relevant organisations to understand what happened and make sure it doesn’t happen again.”