The Victorian arm of Watersun Homes, WSH Group, was recently placed into voluntary administration with $20 million in debts.

Now another collapse could be imminent, leaving further tradespeople with huge unpaid bills.

Watersun Construction, a separate company associated with a number of commercial projects in Melbourne, has seemingly come to a halt.

Calls and other correspondence to the company have gone unanswered, while its registered office at 58 Queens Bridge Street in Southbank has been locked up.

Earlier this year the construction company was building a four-storey apartment complex in Blackburn.

But the site's China-based developer, Queens Apartments, says workers stopped turning up at the site last month.

"The builder, Watersun Constructions, while still trading and legally solvent, has ceased work on the Sovereign Blackburn project," a spokeswoman for Queens Apartments said.

"Watersun has provided no reason nor justification to explain inactivity of site works."

It is also believed Watersun was working on a childcare centre in Barkly Street, Footscray, but work there has come to a standstill.

Lynda Rafferty, an owner of B.R. Demolition, a small family business in Mentone, said the company was owed $50,000 for about five weeks spent at the Footscray site four months ago.

Mrs Rafferty said she had been in touch with a site manager until March, but he had since stopped returning her calls.

She said the site manager told her there was a silent partner interested in buying into the business and covering the outstanding invoices.

"But that didn't happen," Mrs Rafferty said. "Now this guy is not contactable; I think I have left 20 messages for him.

"Because they haven't gone into liquidation, there may be some chance that we may be able to get some money back, but I'm not holding out any hope on it now."

Mrs Rafferty said it was a "big hit" on the business.

"We are really good people; we run a family business, pay our employees above and beyond what they should be paid."

A source from the debt collection industry said he had been contacted by numerous building contractors who had not been paid by Watersun Construction.

"There are multiple sites. They have all stopped, there is no supervisors or foremans," he said.

"No one knows how to contact them, as they shared Watersun's offices. It is not trading, but it is still solvent."

Fairfax Media has been unable to contact Watersun Construction's sole director, Williamstown developer Gary John Caulfield, also a director of Watersun Homes' WSH Group.

Multimillion developer Benni Aroni was also a director of both WSH Group and Watersun Construction until recently. He resigned from the companies in August 2015 and February 2016 respectively.

Mr Aroni hung up before being told what the call was about when contacted by Fairfax Media.

"Sorry, I can't comment," he said.

Another former director, Russell Leonard Berman, resigned in October.

The developer behind the Sovereign Blackburn apartment project said it was in discussion with a new builder and expected only small delays to the 75-apartment project, expected to be completed by late 2017.