The Fire Investigation Unit is examining a pallet fire that occurred in Menangle Park on Tuesday night.
Two trucks, a shipping container full of artificial turf and a forklift were destroyed in the blaze on Racecourse Avenue.
The fire broke out about 8pm and several Macarthur NSW Rural Fire Service (RFS) and Fire and Rescue NSW (FRNSW) crews were called out.
RFS Macarthur operations officer Andrew Pearson said firefighters arrived to find acres of pallets, wood and rubbish alight.
Mr Pearson said the fire generated large volumes of black smoke.
“The smoke could be seen from the top of Douglas Park and in parts of Campbelltown,” he said.
More than 20 firefighting trucks were used and it took crews about two hours to contain the blaze.
Mr Pearson said the fire’s cause remained unknown at this stage.