Hundreds of extra contractors will be on site at BlueScope Steel's Port Kembla plant this week as its last operational blast furnace is shut down for regular maintenance.
The routine shutdown meant the steelworks wouldn't be producing steel for about 60 hours from early this morning, steelmaking general manager John Nowlan said.
Production would then slowly ramp back up to capacity by the middle of next week.
Maintenance shutdowns at the No 5 blast furnace are carried out roughly every six months, most recently in May this year.
Mr Nowlan said now that BlueScope only had one blast furnace, this week's operation had been delayed slightly to coincide with a quieter time in the steel market.
The No.6 furnace was mothballed as part of the company's major restructure last year.
Work to be completed this week would include "small capital works" to improve the raw material feed system, plus monitoring and checks on elements including cooling staves, refractories, dust and scrubbing systems.
The company completed a $370 million reline of the blast furnace in 2009 that was expected to extend its operational life by up to 20 years.
Mr Nowlan said the furnace had operated "very well" since then.
"We're about three-and-a-bit years in. It's operated at full production basically all the way through and it continues to do that," he said.
One issue identified related to a "very small" number of copper staves in the furnace that Mr Nowlan said were being assessed.
"That's just part of what we do as part of managing this furnace," he said. "We have to check wear and we have to check condition on the furnace on an ongoing basis and respond to it."
BlueScope expects to produce about 2.6 million tonnes of steel this financial year.