Witnesses describe horror of seeing six-year-old boy thrown from tenth floor of the Tate Modern

A witness to the alleged attempted murder of a six-year-old boy has described the horror she felt after the boy was thrown from the 10th story of the Tate Modern in London.

BBC journalist Olga Malehevska was on the balcony with her four-year-old when the "absolutely terrifying" attack took place on Sunday.

Malehevska told The Daily Mail she could hear people screaming "Oh my god the boy dropped!"

She says she could hear the boy's mother sobbing and shouting "oh my son, my son."

A 17-year-old boy was arrested on suspicion of attempted murder after allegedly grabbing a six-year-old child and throwing him off the tenth-floor viewing platform of the Tate Modern. 

The child landed five floors down on an adjacent rooftop.

The BBC reported the boy was a French tourist to the city. 

Everyone was kept inside the building, and Malehevska said she could see the teenager who threw the child being restrained by people in the gallery

Witnesses told The Telegraph an angry bystander attacked the suspect and punched him in the face before members of the public locked the teen in a public toilet for his own safety. 

"He didn't fight back, he didn't shout or anything," Malehevska told The Daily Mail.

"He was just emotionless. The whole situation was terrifying, we are so shaken."

Another witness claims the teen followed her and her family through the gallery, taking photos of her children.

She described the teen as white, with scraggly hair and a beard.

The six-year-old boy remains in hospital in a critical but no longer life-threatening condition, according to Metropolitan Police.