A boy, 12, died and his 18-year-old sister was hospitalised with "poisoning" after vaping together, police say.
The sister's friend, 17, was also in a critical condition following a sleepover.
The trio were found unconscious in an apartment in Biysk, Russia the following morning after the vaping session.
Schoolboy Denis Shnayder could not be saved and his sister’s friend, identified as Anastasia R, was in a coma with her life under threat.
His sister Viktoria, a student, was also hospitalised after the trio were found by Anastasia’s grandmother in the morning.
“They had all consumed smoking mixtures with an electronic device,” Lyudmila Ryazantseva, from the Russian Investigative Committee, said.
“They were found unconscious the following day.
“The girls were rushed to hospital.
“Unfortunately the boy could not be saved.”
The girls remain in hospital, with Anastasia in intensive care.
A criminal case has been opened into causing death by negligence and an inspection into whether there was a failure of parental supervision.
Viktoria had posted under a video on social media: "I vape all day long until I feel sick.”
The case has prompted demands for tougher controls on vaping by young people.
“If children are dying from vaping, then the current law equating this to cigarettes is not enough,” MP Denis Svishchev, head of the Russian parliament’s sports committee, said.
“We need a complete ban on vaping.”
Another MP Sultan Khamzaev has called for a total ban on vaping and tobacco-related products for children.
The group were using e-cigarettes to inhale a vapour from nicotine, flavourings and chemicals.
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