A teenager has been arrested after allegedly throwing a six-year-old boy from a tenth-floor viewing platform of London's Tate Modern gallery.
The victim is in a critical condition in hospital after being found on the fifth-floor roof, the Metropolitan Police said.
The 17-year-old male suspect had remained with members of the public on the tenth-floor viewing platform after the incident on Sunday afternoon, the force said.
They added that there is nothing to suggest that he is known to the victim.
Officers had been called to the gallery at around 2.40pm and the child was treated at the scene before being flown to hospital by London's Air Ambulance.
Visitors reported on social media not being allowed in or out of the gallery while emergency services dealt with the incident.
Scotland Yard said a number of members of the public are assisting police with witness statements and visitors to the gallery have been allowed to leave.
BBC journalist Jonny Dymond, who was in the gallery at the time, said visitors were funnelled into the main hall while all exits were closed.
He added: "There were quite a lot of families with children, and security guards told us we couldn't leave.
"There were at least two fire engines, ten police cars and an incident control unit.
"Parts of the exterior of the building were taped off."
A London Ambulance service spokesman said: "We treated a person at the scene and took them to hospital as a priority."
The Tate confirmed that it would be closed for the rest of today.
The Tate Modern was the UK's most popular tourist attraction in 2018 after being visited 5.9 million times, according to the Association of Leading Visitor Attractions.
