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 but Hampshire Constabulary are investigating the circumstances.
The festival has cancelled the second day of the event, which was to be headlined by Craig David and Sean Paul, after warning of a "dangerous high strength or bad batch substance on site".
We can confirm that two people have died after falling ill at Mutiny Festival in Portsmouth.An 18-year-old woman and...
The announcement, which organisers said was a "safety precaution", prompted demands for refunds from disappointed customers on social media.
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 social media accounts said: "Mutiny Festivals are devastated to hear of the tragic loss of life from its festival family today."
It later added: "Following the terrible news from earlier today, the team behind Mutiny Festival are incredibly sad to announce that the Sunday of the festival has been cancelled as a safety precaution.
"The safety of our amazing customers has always been paramount to us and so to keep everyone safe and in respect to those who have passed, we have taken the decision not to open today.
"As you can imagine, this decision was not taken lightly and was taken with the support of the local statutory authorities who we continue to work with."
The organisers also urged customers to "responsibly dispose" of any substances.
Following the terrible news from earlier today, the team behind Mutiny Festival are incredibly sad to announce that the...
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.