Two health and safety inspectors are at the scene of last night's factory fire in South Auckland and will make a decision over whether the plant should stay open.
Six workers were in the National Steel scrap metal plant in Wiri when the incident began with an explosion shortly after 7pm.
The Fire Service believes it was caused when an LPG bottle inside a car being processed blew up.
A spokeswoman for the Ministry of Business Innovation and Employment said officials attended the scene last night and two health and safety inspectors are there this morning.
"They are looking at what happened and assessing the health and safety systems in the workplace. Once the assessment is done a decision will be made as the whether the plant should be closed or not.''
Workers were lucky to escape without injury the Fire Service said.
"The occupants of the premises are extremely lucky given the force the of the explosion that they weren't in an area that they [could have been] seriously injured or even worse,'' Auckland acting commander Roger Callister told Radio New Zealand.
The fire took about 15 minutes to get under control.
According to its website, National Steel, processes various metals, including aluminium, copper, steel and stainless steel in various forms such as car bodies, whiteware, building materials, cans, and cables.
Owner Roshan Nauhria said staff had told him there was minimal damage to the building.
Although the Fire Service believed an LPG bottle was to blame, Mr Nauhria said it was possible there was still some petrol in a vehicle going through the shredder.
"We check every car and sometimes you miss a petrol tank or something,'' he said.
"When we started we used to have a blast, more or less one every week - now we probably have a blast, one every two months, three months.
"We take a lot of precautions,'' Mr Nauhria said.