Two people, including a 14-year-old boy, have been arrested on suspicion of raping a young woman at Reading Festival.
The 19-year-old victim reported being subjected to the sex attack in a caravan on the festival traders' site last night.
She had earlier met a man and a boy near an ice cream van opposite a mobile phone charging point in one of the campsites.
A boy of 14, from Surrey, and a 31-year-old man from London were being held in police custody on suspicion of rape, Thames Valley Police said.
The arrests emerged as festival-goers started pouring in to see acts this weekend including Arctic Monkeys, Blink-182 and Paramore.
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 so far, 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."