A 17-year-old girl was raped by a man thought to be in his 50s at an August Bank Holiday motorsport event in Herefordshire.
The attack happened on Monday at an autograss meeting, being held off the A44, at Monkland, near Leominster.
Police said the site was busy with people camping as part of the three-day event. They said they were working with organisers to find the man.
Officers said the attack was an "unusual event" for the county.
Detectives said they were particularly keen to speak to anyone who was in the beer tent immediately before the attack.
They said it was believed a fight had broken out there.
'Serious incident'
Det Ch Insp Sheila Thornes said: "This is a serious incident and police are keen to trace the offender as quickly as possible.
"People were attending the event from around the country as well as from the local area and it is important that we speak to anyone who can assist the investigation.
"I must stress that this is an unusual event for Herefordshire and we are continuing to liaise with members of the autograss community as well as the victim and her family to provide all of the appropriate reassurance and support."
The man is described as white, about 5ft 9in tall with short, spiky grey hair.
He wore a dark zip-up top, smart trousers and lace-up shoes similar to walking boots.
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