That fire eventually ignited Reid Boiler Works, an old industrial building on the waterfront.
When fire crews arrived on scene, they found the business fully involved by fire, with flames shooting through the warehouse roof.
The nearby railway was closed because of the intense heat and flames.
The stubborn fire took nearly 90 minutes to fully extinguish.
The fire investigation identified three gold-colored aerial fireworks had been discharged just south of Reid Boiler Works before the grass fire was reported.
No fire damage costs have been released.