A large fire that sparked in BlueScope Steel's recycling area on Friday afternoon was extinguished late Saturday.
The fire started when timber pallets ignited for an unknown reason about 1.30pm on Friday.
Fire and Rescue NSW Inspector Jay Bland said the blaze was finally put out at about 3pm on Saturday.
NSW Fire and Rescue personnel, and a Serco industrial crew, blanketed the fire with water and foam for more than 24 hours.
Insp Bland said their efforts were hampered by the "deep-seated nature" of the fire, with a dozer brought in to pull away the material so crews could get to the heart of the blaze.
Smoke billowed across much of Port Kembla on Friday, and flames up to 20 metres high could be seen from Five Islands Road.
Insp Bland said it had been one of the most protracted incidents in the region for a number of years, and credited the quick actions of fire crews for preventing the fire from spreading further.
A BlueScope spokesman said the smoke was not toxic.
"The fire has been fuelled by clean timber waste only [non-toxic timber pallets], and the cause will be the subject of an investigation," he said. "There have been no injuries or significant damage to any plant or equipment."