Hamilton police detectives are keen to speak to anyone who was at Nigretta Falls, west of the city, on Friday afternoon and night.

Detective Sergeant Mark James, of the Hamilton police crime investigation unit, said the investigation into the cause of a fire that burnt about 30 hectares was continuing.

He said it was believed that the fire started early Saturday morning after people had left the area.

"We are trying to speak to everyone who was there Friday afternoon and evening so they can be eliminated from the inquiry," he said.

"Anyone with relevant information is requested to contact the Hamilton police CIU on 55519150 or Crime Stoppers on 1800 333 000," he said.

Monday, 9.30am:

Southern Grampians Shire Council has advised the public reserve has been closed due to a fire over the weekend.

"There is currently no access to the viewing platform, public toilets or barbecue area until further notice," a statement by the council said.

"The area has been closed due to on-going investigations and for Occupational Health and Safety reasons."

EARLIER, JANUARY 28:

Police are investigating a suspicious fire near Hamilton's Nigretta Falls on Friday night.

The blaze damaged about 30 hectares of land.

A Victoria Police spokeswoman said Portland Crime Investigation Unit detectives were investigating the incident.

"It's believed bushland in a reserve off Nigretta Falls Access Road caught fire and spread to adjoining paddocks about 2.30am," the spokeswoman said.

"Investigators were told up to 30 hectares were burnt before being contained.

"The fire is being treated as suspicious and an investigation into the incident is ongoing."

Bainbridge CFA volunteer firefighter Hardy Clemens said crew members were called to the fire at about 2am.

"The fire was so big it could be seen from our shed," he said.

"It's not a good thing to see. It will be a long day for the 20 plus crew that turned out and many, many hours of blacking out to go."

He said it took firefighters about five hours to contain the fire, with volunteers remaining on site to black out the fire.

Anyone who witnessed the fire or with any information is urged to contact Crimestoppers on 1800 333 000 or submit a confidential report online at www.crimestoppersvic.com.au.

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