Victoria police spokesperson Senior Constable Melissa Seach said the man, 35, entered a tent on Jack Smiths Lane, Lexton, 50 kilometres north-west of Ballarat, at 9.30am and indecently assaulted a woman. 

The South Melbourne man was assisting police with their inquiries and is yet to be charged, Senior Constable Seach said. 

The popular four-day festival has been marred by controversy over recent years, with a man dying from a drug overdose in 2012 and five others admitted to hospital following excessive drug consumption in 2010.

The mother of 34-year-old Daniel Buccianti, who died in 2012, recently urged revellers to be safe ahead of this year's festival.

Ambulance Victoria spokesperson John Mullen said three people were transported to Ballarat Base Hospital on Saturday for suspected overdose

One male, in his 20s, was unconscious and in a serious condition when he was taken to hospital at 4.20am on Saturday, Mr Mullen said.

The festival, which attracts more than 10,000 people from Victoria and interstate, concludes on Monday.