A six-year-old boy is in critical condition after he was allegedly thrown from the 10th story viewing platform at London’s Tate Modern on Sunday afternoon. A 17-year-old male, who was unknown to the child, has been arrested on suspicion of attempted murder.

Emergency services were called to Tate Modern shortly before 3 p.m. on Sunday, August 4, after the boy fell five stories and landed on a roof on the gallery’s fifth floor. The child was treated at the scene before being rushed to hospital by an air ambulance.

The young boy is no longer in life-threatening condition. London’s Metropolitan Police Service has issued a statement this morning that his condition has been assessed as “critical, but stable.”

Witnesses heard a loud bang, followed by screams from the boy’s mother. Members of the public present on the platform detained a man, who eye-witnesses say remained “quite calm.” 

A London Air Ambulance helicopter takes off from outside the Tate Modern gallery in London on August 4, 2019 after it was put on lock down and evacuated after an incident involving a child falling from height and being airlifted to hospital. Photo by Daniel Sorabji/AFP/Getty Images.

“A 17-year-old male had remained with members of the public on the tenth floor viewing platform,” a statement from the police explains. “There is nothing to suggest that he is known to the victim. The teenager was arrested by police officers on suspicion of attempted murder and taken into police custody.” 

One line of inquiry into the incident is the mental health of the suspect, the Guardian reports.

Following the incident, museum visitors were directed downstairs to the museum’s Turbine Hall, and were kept inside the building as ambulances and police attended the scene. The Tate closed for the remainder of Sunday, with the museum posting a notice on Twitter about the incident.

“Tate is working closely with the police,” a museum spokesperson wrote, adding, “All our thoughts are with the child and his family.” The gallery is open today, although the viewing platform is closed.

In 2007, a young lawyer fell to his death from a different high-level balcony. The coroner’s verdict was accidental death, although there was evidence that the 27-year-old had been suicidal. A senior banker, who was 48, died after falling from another balcony in 2012. The coroner ruled that there was “no evidence of intent or suspicious circumstances.”