A 14-year-old boy is one of two people arrested on suspicion of rape at Reading Festival.
A 19-year-old told police she was attacked in a caravan on the festival traders’ site on Thursday night.
She had earlier met a man and a boy near an ice cream van opposite one of the campsites.
The 14-year-old, from Surrey, has been detained along with a 31-year-old London man, Thames Valley Police said.
The arrests emerged as an estimated 90,000 music fans began arriving to see performances this weekend by acts such as Arctic Monkeys, Blink-182, Jake Bugg 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.”
There have been 21 crimes at the Richfield Avenue site so far, police said. Five of these were alleged drugs offences and 13 were suspected thefts.
Mr Parker added: “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.”
Police have urged anyone heading to Reading to monitor their festival Twitter page for safety information and messages.
Anyone with any information about the alleged rape is asked to call police on 101.