The 21-year-old was at the Rainbow Serpent Festival outside Ararat in south-west Victoria when an unknown man grabbed her by the throat, pushed her against a van and assaulted her.

The woman managed to get away but the man grabbed her and sexually assaulted her another two times. The attacker also bit the woman twice on the arm when she tried to push him away.

Police are appealing for festivalgoers with more information to come forward about the incident, which took place between 3pm and 7pm on January 26.

According to police, the woman had been walking along the outer edge of the festival's camp section when she struck up a conversation with the man.

After a short conversation, the victim told the man she was going to the main festival area when he grabbed her by the hair and throat and assaulted her.

Police have raised concerns about the future of the six-day festival, which has a chequered history of fatal drug overdoses and sexual assaults.

Last year, more than 40 revellers were caught driving under the influence of drugs when leaving the festival.

Superintendent Andrew Allen said police remained concerned about the behaviour of festivalgoers, telling Fairfax Media he would be "agitating for a reduction in the length of the festival with the organisers".

"The harm to the wider community is at such an alarming and tragic cost," he said.

"Something has to change."

In January 2016, police reportedly dealt with four sexual assaults at Rainbow Serpent. In December, organisers of the festival launched what was touted as an Australian-first policy to handle sexual assaults at the festival.

A digital image of the man wanted for questioning has been released. He is described as about 28-years-old with sandy brown hair, blue eyes, a pointy nose, and between 165 to 170 centimetres tall.

- with Ballarat Courier.