Police have arrested two people, including a 14-year-old boy, on suspicion of raping a young woman at Reading Festival's campsite on Thursday night.
The 19-year-old victim reported being subjected to the sex attack in a caravan on the festival traders' section of the campsite last night.
She told the authorities she had met a man and a boy near an ice cream van opposite a mobile phone charging point in one of the campsites for festival goers earlier that day.
A boy, 14, from Surrey and a 31-year-old man from London are being held in police custody on suspicion of rape, Thames Valley Police said.
The arrests emerge as crowds begin pouring in to see music acts this weekend. Performers include Artic Monkeys and Blink 182. The campsite has been open since Wednesday for attendees to set up camp ahead of the music festival that officially starts tonight and runs over the Bank Holiday weekend.
Chief Inspector Dave Parker said: "There is currently a scene watch in place and I would like to reassure those attending the festival that crime levels remain low and crimes of this nature are very rare.
"Officers are patrolling the site to support on-site security and if anyone has any concerns, please feel free to approach our officers to discuss these."
Police said there have been 21 crimes at the festival site since Wednesday, including five alleged drugs offences and 13 suspected thefts.
Mr Parker said: "I know many people will be celebrating their A-level and GCSE results and officers are working to make sure this is a safe environment in which to have fun."