A 16-year-old girl has died after taking a "yellowy-white" paste thought to contain amphetamine, police said on Friday.
A man and a woman have been arrested in connection with the teenager's death, prompting North Yorkshire Police to issue an urgent health warning.
Paramedics were called to a property in Tang Hall Lane, York, on Thursday night and the girl was rushed to York District Hospital in an ambulance at around 11.30pm.
But the teenager died in the early hours of this morning, despite attempts to resuscitate her.
A 21-year-old man is in a "serious but stable condition" at the same hospital after being taken in by a friend at around midnight in a related incident.
A 23-year-old man and a 26-year-old woman, both from York, have been arrested in connection with the investigation and remain in custody for questioning.
Police said the substance involved is undergoing tests but it is believed to contain amphetamine.
The force issued the following safety warning: "In relation to this investigation, North Yorkshire Police and the North Yorkshire and York Primary Care Trust are urging anyone with drug-related health concerns to seek medical assistance without delay.
"Either contact your GP or go to straight to hospital if required.
"The yellow/white paste involved in this particular case is undergoing tests to determine exactly what it contains, although amphetamine is believed to be involved.
"Until this is confirmed, people are strongly urged not to risk taking substances matching this description or of a similar nature.
"One girl has already died and a young man is in a serious but stable condition at hospital, so the potential dangers are very real."
Police said inquiries were continuing at the address in Tang Hall Lane and witnesses or anyone with information is urged to contact North Yorkshire Police.
Neighbours spoke of their shock at the death.
Simon Moss, chairman of Tang Hall Residents Association, said there had been problems at the property with loud music and people calling at the house at unsociable hours.
He said: "I heard fireworks at 10.30pm yesterday. They were really loud. Later I heard the sound of a house alarm and car alarm going off. Later I saw the ambulance parked outside. As you can see from the window there has been trouble before and I think the front door was knocked in on one occasion."
He said he thought a woman lived at the property with four children.
Neighbour Tom Gibson also heard loud music and fireworks being let off last night.
He said a woman and three girls lived at the address but the children had recently gone to live with their grandmother and had not been seen for 18 months.
He added: "The ambulance arrived just after midnight. I presume they were working on someone in there."
"It is an absolute tragedy. I really feel for the parents of the girl. Apart from last night there has been nothing unusual, apart from on occasion a bit of noise."
It is thought the dead girl, who has not been named, lived locally and attended the property last night.