(CNN) A teenager has been arrested on suspicion of attempted murder after a boy was thrown from the 10th floor at the Tate Modern gallery in central London on Sunday, the city's Metropolitan Police said.

The 6-year-old was found badly injured on a fifth-floor roof and was taken to a hospital by a helicopter, police said.

Officers initially said the boy was in critical condition. In an update on Monday, they said he was in "critical but stable condition." They added the boy's family was being supported by police.

Police said the 17-year-old male suspect had remained with members of the public on the 10th-floor viewing platform and was taken into police custody.

"There is nothing to suggest that he is known to the victim," the statement added.

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