Firefighters have battled a 200-tonne molten spill, high gas levels and fires at the Glenbrook Steel mill near Auckland.
Crews were called to the site about 8.30pm on Thursday when one of the tanks began to overflow.
The station officer at the Waiuku Volunteers Fire Brigade says no one was hurt and the various problems were dealt with quickly.
Kevin Wanhill says there have been three or four similar incidents in the past two years, but would not speculate on why the problems keep arising.
