An 18-year-old woman and a 20-year-old man have died after falling ill at the Mutiny Festival in Portsmouth on Saturday evening.
The deaths are being treated as separate incidents and are not being treated as suspicious, however Hampshire Constabulary said inquiries are being made to determine the circumstances.
The festival issued a “harm prevention alert” via social media on Saturday night warning of a “dangerous high strength or bad batch substance on site”.
Dizzee Rascal, Craig David and Sean Paul top the bill at the two-day event that ends on Sunday.
Police were first alerted to the woman falling ill at the site on Saturday evening and the man was found collapsed around 20 minutes later.
Both were taken to the Queen Alexandra Hospital where they later died.
A statement posted on the music festival’s Twitter page said: “Mutiny Festivals are devastated to hear of the tragic loss of life from its festival family today.
“Our thoughts and prayers are with the family and friends at this very difficult time and we will continue to work with the authorities to support them in any way possible.”
In a message posted on social media after the pair were taken ill, organisers warned of a dangerous substance circulating on site and urged revellers not to take anything.
Police have appealed for anyone with information to come forward.
The force said: “At 7.10pm on Saturday 26 May, we were informed that an 18-year-old woman had fallen ill at the festival site in King George V Playing Fields, Cosham.
“The woman was taken to Queen Alexandra Hospital where she later died.
“At 7.30pm, a 20-year-old man was found collapsed at the festival site. He was taken to Queen Alexandra Hospital where he later died.
“The deaths are being treated as separate incidents at this stage. They are not being treated as suspicious but inquiries are being made to determine the circumstances of what happened in each case.”
The force said next-of-kin for both the woman and the man had been informed and were being supported by specialist officers.
Anyone with information is asked to contact police on 101.