The teenage girl who died after collapsing at Oxford's Hinksey Park is thought to have taken the substance MDMA, more commonly known as the drug Ecstasy.

Thames Valley Police is continuing to investigate the unexplained death of the teenager who suffered a cardiac arrest while at the park off Lake Street, South Oxford, at about 1.15pm yesterday.

The force has now identified the girl as 15-year-old Martha Fernback, from Oxford, and today floral tributes have been placed in the park opposite South Oxford Community Centre.

Senior Investigating Officer Det Insp Brendan Murray said: “Firstly our thoughts are very much with Martha’s family, who have been left devastated and distraught by her death.

“Following our initial enquiries we now understand Martha had taken a substance earlier that day which she believed was MDMA.

“It would be wrong to speculate on what this substance was or what caused her death, as the investigation is still at an early stage.

“A full post-mortem examination will be carried out tomorrow, which will include toxicology tests.

"It is likely to be several weeks before the results of these tests are known.

“I would strongly urge young people not to take or experiment with illegal drugs such as MDMA.

"They are extremely dangerous and often contain poisons and illicit chemicals which can prove fatal.”

If you have information which could assist the police inquiry, please call CID in Oxford on the 24-hour police enquiry line on 101 or the Crimestoppers hotline on an anonymous 0800 555111.

Police are publicising FRANK, a confidential drugs advice helpline for young people, which can be reached by calling 0800 776600 or by visiting: talktofrank.com

A 17-year-old boy from the Oxford area has been arrested on suspicion of possession with intent to supply a controlled drug, in connection with the ongoing investigation, and he is currently in custody for questioning.