When asked by Melbourne reporters if seat belts should be made compulsory, Mr Andrews said: "I can assure all Victorians that there will be a proper thorough review of what has gone on.

“If there are learnings and things that need to be changed as a result of that then we stand ready to make such changes."

As Victorian law stands, passengers must wear seat belts if a vehicle is fitted with them. 

There is no mandatory or legislative requirement for buses, whether state or privately run, to have seat belts if they began operating before 1992.

But an Australian design requirement means all new coaches that entered service after 1992 must have them installed.

The government will await the findings of both a police and coronial investigation before announcing if there will be any changes to the rules.

Major Collision Investigation Unit detectives travelled from Melbourne to the crash site along the Sunraysia Highway on Saturday, remaining late into the night after Creswick woman Carmell Mitchell died.

Mr Andrews made a heartfelt thanks to Saturday's first responders, which included police, firefighters, paramedics and SES crews who live across the Ballarat region.

"Our thoughts and our prayers and our best wishes go out to the family of (Ms Mitchell)," he said.

Emergency crews spoke of a “chaotic” scene in the moments after the bus came off the road just opposite a residential house north of Avoca.

Many passengers were hanging from their seat belts after the vehicle flipped.