Riverina Police District's Inspector Peter McLay said they were investigating whether fire had been deliberately lit, urging anyone with information to come forward.

"About 2.10pm on Thursday, emergency services responded to a large fire at the derelict south campus buildings off Fernleigh Road," he said.

"Anyone who was in the area or who has dashcam footage from 1.30pm to 2pm ... we are urging them to come forward.

"We are treating this fire as suspicious."

Another section of the old campus was ravaged by flames in April this year, and Inspector McLay said they were not ruling out connections between the two incidents.

The investigation into the April fire is still ongoing.

The land is now owned by Signature Care, who are planning to build an aged care centre.

CFO Stephen Pollock said the fire, as unfortunate as it was, will not have any impact on the company.

"We are still in the process of trying to get approval from council," he said.

"We are in the middle of compiling reports and paperwork they are asking for.

"We will demolish the derelict buildings on approval."

FRNSW zone commander Stewart Alexander said crews finished up at the site on 7pm.

"We handed it over to NSW Police, and they will be conducting an investigation," he said.

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"They will be calling on us for more information, but at this point, we are not sure of any cause or origin."

Superintendent Alexander said emergency services worked together efficiently to deal with the threat.

"They should be commended in preventing the spread of the fire to the rest of the building if it had spread we would have still been there," he said.

"All the emergency workers come together in a regional area which is great. We are all on the same page."