Officers were called by the ambulance service to a report that a girl had become unwell at an address in the North Marine Road area of Scarborough at about 4pm on Wednesday May 20.
On attendance, two teenage girls were found taken by ambulance to hospital.
Tragically, a 14-year-old girl was pronounced dead at hospital a short time later and a 13-year-old girl remains in hospital. Her condition is not believed to be life-threatening.
Police are appealing for information and have issued a warning about illegal drugs after the girl's death.
Two teenage boys have been arrested by police on suspicion of offences involving the supply of Class A drugs.
One has been released under investigation and the other remains in custody at this time.
Detective Chief Inspector Graeme Wright, of North Yorkshire Police, said: “First and foremost, our thoughts are with the family and friends of the young girl who died as a result of this tragic event, and of all those affected by it.
“Extensive police enquiries are ongoing to determine the events around her death.
“Although our investigation is at an early stage, I would urge anyone who has acquired MDMA or other illegal drugs recently not to take them. If you have taken such a drug and feel unwell, it is vital that you seek medical help immediately.
“This is clearly a devastating incident, and I would ask everyone to respect the privacy of the families involved, and refrain from speculating about this incident online.”
Anyone with information about the incident, who has not already spoken to police, is asked to contact North Yorkshire Police on 101, quoting reference 12200084012.
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