Police were called when a fight involving about 15 men and women broke out in the hotel carpark around 8.30pm.

During the fight a man allegedly drove a car into the group and injured four people.

Two women were taken by ambulance to the Ballarat Health Services Base Hospital with minor injuries.

Police also discovered a firearm that had been discarded close to the scene of the fight.

Bacchus Marsh detective Brian Mallock said police were interviewing three people last night and firearm, affray and assault charges were expected to be laid.

"It appears there was some talk inside and the fight was taken outside the pub into the carpark, where a car drove through the group," he said.

"A firearm, which we don't believe was used in the fight, was also found by police close by."

Ten units from Ballarat, Ballan, Moorabool, Linton and Bacchus Marsh attended.

Five units originally attended the incident before more were called to provide support.

Police also based themselves on roads in Lal Lal leading to the site.

The fight had broken up by the time police arrived.

Sgt Mallock said he believed members of the Bandidos motorcycle gang were involved in the incident.

Ballan sergeant Ken Tingate said he expected the investigation to be a long one.

Last night police were interviewing numerous witnesses to the incident.

"It will be an ongoing investigation," Sgt Tingate said.

The Bacchus Marsh CIU will continue the investigation.