A fire has destroyed workshops and vehicles at the Struan Research Centre, 16 kilometres south of Naracoorte in South Australia's South East.
It follows three blazes in six months at the site owned by South Australian Research and Development Institute (SARDI).
The Department of Primary Industries and Regions is finalising the insurance claim for the first and most significant blaze in November 2022, when fire destroyed the main research centre and labs, estimated by the Country Fire Service (CFS) to have caused $5 million at the time.
Two other fires started in the weeks following the initial blaze.
Latest fire possibly 'deliberate'
CFS crews from Naracoorte, Penola and Mount Gambier were alerted to the fire just after 11pm on Wednesday night.
On arrival, 34 volunteer firefighters on 10 CFS trucks found two trucks and a tractor, and a shed containing another three vehicles, alight.
Crews spent approximately four hours extinguishing the fire but were unable to save the vehicles and sheds.
Crews prevented the spread of the fire into adjoining sheds, and the historic 1875 Struan House remained undamaged.
Two CFS crews were called back to the site in the early hours of Thursday morning, following a flare-up.
Total losses from the fire are estimated to be around $700,000.
Fire Cause Investigators and police will commence work to determine the cause of the recent fires.
Region 5 duty officer Damon Whitwell told ABC South East it was "too early" to tell if the fire had been deliberately lit, however executive director of SARDI and major programs' Peter Appleford told ABC Adelaide he believed it was "deliberate".
"The first fires were investigated and when everything's burned down it's very difficult to work out what happened and there were no suspicious circumstances identified," Mr Appleford said.
He said, in this instance, it appeared as if the vehicles and shed were lit from the inside.
Staff 'suffering the most' as fourth fire erupts
Mr Appleford said staff morale had taken a hit in the months since the initial blaze and during the subsequent incidents.
"It wears on the staff down there; it's really hard on them," he said.
"We've lost a bit of equipment and had to re-start a couple of trials."
Mr Appleford said more security had been put in place at the site, but some areas remained without upgraded surveillance.
No-one was injured in the fire, and police have asked anyone with information to contact Crime Stoppers on 1800 333 000.
