The fire broke out on Thursday at the Eco Special Waste Management plant in the Tuas industrial district, bordering Malaysia, fuelled by chemical waste and other flammable materials, officials said.
Videos and photos acquired by Reuters showed a large flame and a tall column of dark smoke covering part of the sky.
Periodic explosions were heard as firefighters battled the blaze with foam, the Singapore Civil Defence Force (SCDF) said in a Facebook post.
One firefighter needed hospital treatment for exhaustion, a SCDF spokesman told Reuters, adding the fire had been brought under control.
After an initial assessment, about half the plant had been damaged, chief executive Rick Reidinger told media.
The company could not be immediately reached for comment.