The closure of steelmaker Arrium would cause Australia's construction industry to collapse within six weeks, its administrator says.

“The impact would be felt far and wide. Arrium long-form structural steel makes up 70 per cent of Australian steel making in infrastructure and construction,” KordaMentha’s Mark Mentha said.

“When you’re talking about billion-dollar projects, delivery for steel would be 18 months or more in advance. The impact of not having steel – you’d have to find alternatives in the global market place.”

But peak industry body Master Builders South Australia said Mr Mentha’s claim was overblown as the industry had access to other domestic steel providers including BlueScope.

“Building and construction won’t collapse or be devastated by the closure of Arrium but it will be hit,” chief executive Ian Markos said.

He also said the “most dangerous” outcome of an Arrium collapse would be the forecast loss of almost 4000 jobs in the Whyalla region on the Eyre Peninsula, where its steelworks are based.

KordaMentha on Monday revealed that the restructuring and sale of the Arrium group, which went into voluntary administration last month, would likely be complete by the end of the year.

The SA government said it was considering a “substantial” plan from the administrators to save the steelworks.

And KordaMentha expected the Arrium group of companies to attract genuine interest from a number of credible local and international parties.