Four stables at Greymouth racecourse caught fire overnight.
The Fire Southern Communications Centre received a call about the fire at 3.42 am, shift manager Andrew Morris said.
"They sent two fire engines and a support vehicle. The support vehicle carried extra guys."
On arrival, firefighters found four stables with an area of some 100sq m ablaze.
The stables had no horses in them and the fire was extinguished.
"It is being treated as suspicious," Mr Norris said.
Mr Norris said West Coast fire investigator Dan Green planned to attend the scene this morning, along with police.
The racecourse hosted the Interislander Summer Festival earlier this year.
