A teenager has been arrested on suspicion of attempted murder after a six-year-old boy was thrown from the 10th-floor viewing platform at the Tate Modern, police have said.
The child was taken to hospital by the air ambulance after being found on a fifth floor roof and is in a critical condition, the Metropolitan police said.
A 17-year-old boy remained with members of the public on the viewing platform and was arrested by police officers and taken into custody.
â€œThere is nothing to suggest that he is known to the victim,â€ the Met said in a statement.
Visitors to the gallery said they were kept inside as officers dealt with the incident, while others posted images of firefighters outside the gallery on the South Bank in central London.
A Met police statement posted on Twitter said: â€œOfficers are in the vicinity of the Tate Modern following an incident this afternoon. A child fell from height and is being taken to hospital by Londonâ€™s air ambulance. We await an update on his condition. A teenager has been arrested in connection with the incident.â€
The Tate Modern was the UKâ€™s most popular tourist attraction in 2018 after being visited 5.9m times, according to the Association of Leading Visitor Attractions, and would likely have had thousands of visitors on Sunday.
Greg Ritchie posted images on Twitter of the air ambulance landed outside the western entrance to the Turbine Hall area of the gallery.
Another eyewitness, using the Twitter handle Ms Oâ€™Mahuncy, posted a video recorded from within the gallery of the air ambulance taking off. She later posted that visitors had been told they could leave.
A London ambulance service spokesman said that after they were called at 2.40pm two ambulance crews were sent to the scene, along with the hazardous area response team and the air ambulance.
â€œWe treated a person at the scene and took them to hospital as a priority,â€ the spokesman said.
A sign placed outside the gallery confirmed it would be closed for the rest of Sunday.