Parents are being warned over a sinister social media trend their teenagers could be taking part in.
A Chester high school has sent out a letter to raise awareness of the 'dangerous' Blue Whale game.
Participants are encouraged to complete a self-harming task every day for 50 days.
Its final 'challenge' is to commit suicide.
All these actions have to be filmed and shared via social media.
The game started in Russia where it has been linked to the deaths of two youngsters, the Cambridge News reports .
Upton High School have circulated a letter to parents warning them about its dangers.
Deputy head John Keegan wrote: "I want to draw your attention to the Blue Whale game.
"It is a dangerous game that is popular at the moment in Russia and spreading across Eastern Europe. The game is played online and spreads through social media.
"As the game goes on the players are encouraged to self-harm and the final challenge is to commit suicide.
"The game is being played by children of all ages, some as young as primary age, but predominantly by teenagers."
Police officers in Britain are now posting warnings on Twitter and other platforms to alert parents.
Lead youth engagement officer at Cheshire Constabulary, PC Liz Stanton, said: “Cheshire Constabulary is aware of a ‘so-called’ online challenge targeting young and vulnerable people.
“While we have received no reports about this, we would always urge parents to remain vigilant, be aware of what sites/applications their children may be accessing online, and report any concerns they may have.
“Young people are urged to block or not respond to anything online that makes them feel upset, uncomfortable or threatened.
“Our youth engagement officers have been briefing local schools to ensure they are aware of this.
“Anyone with any concerns, is urged to contact police on 101”
The challenge is thought to be named after the common belief blue whales voluntarily wash up on beaches to die.
As part of the ‘game’ the self-harm tasks are set out by someone dubbed the 'master or teacher' of a group on social media.
One of the tell-tale signs a youngster is playing the game is if they carve a whale on their hand.
- Samaritans (116 123) operates a 24-hour service available every day of the year. If you prefer to write down how you’re feeling, or if you’re worried about being overheard on the phone, you can email Samaritans at email@example.com.
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