There were angry scenes as subcontractors tried to retrieve their tools from a locked building site of a major WA construction firm, which yesterday flagged financial difficulties, sending shockwaves through the industry.

Cooper & Oxley, which has worked on both private and government contracts worth hundreds of millions of dollars, sent a letter to subcontractors advising them to cease work as the company was not in a position to pay them.

The letter, seen by the ABC, said the firm was reviewing its financial viability.

Police ordered security guards to let tradies onto the site to retrieve their equipment. ( ABC News: Rebecca Trigger )

Several subcontractors returned this morning to the 500 Hay Street site in Subiaco — a partially built hotel, office space and restaurant precinct — demanding access, at one point pushing over a fence, as private security guards tried to stop them taking tools and equipment.

Police officers arrived and told the guards to let the workers in, saying they were entitled to their tools.

Tradies left blindsided

Ceiling fixing apprentice Sam Hodges said he had only just paid off his tools, so was relieved to be able to retrieve them.

"I came to work on Monday morning, and before I could even get in my mate called to say they had locked it up," he said.

Ceiling fix apprentice Sam Hodges went to the Cooper & Oxley site to retrieve his tools. ( ABC News: Rebecca Trigger )

Ceiling fixer Liam McGlore had been working on the project for more than a year.

He said he had always been paid on time and had no idea the lockout was coming.

When he arrived this morning, security told him he could not enter.

"They were just saying you can't come in, it's trespassing, and we said it's hardly trespassing … we're not trying to steal tools, we're just trying to get our own tools," he said.

Police arrived and told security officers to allow the workers in. ( ABC News: Rebecca Trigger )

Offers of help refused

The project's owners, Singapore-registered firm Dradgin, said in a statement they were unaware the shutdown would occur, and were "very disappointed" with the current situation.

"All payment terms and conditions of the contract have been met by Dradgin Pte Ltd," the statement said.

"In fact, Dradgin offered financial assistance to Cooper & Oxley to help Cooper & Oxley meet its obligations, unfortunately this was not accepted.

"Dradgin's priority is working with all parties involved — including subcontractors — so that the project may be completed as soon as possible."

WA Premier Mark McGowan said it was "pretty rotten" that workers had been locked out.

"Locking the gates, so people couldn't go and get their tools, was pretty bad and I expect people would be very upset by that," he said.

"I don't know if it's lawful or not."

Cooper & Oxley today issued a one-line statement, saying it was making arrangements for all subcontractors to collect their equipment and hardware from their sites.

Who are Cooper & Oxley?

The Cooper & Oxley worksite at Hollywood Hospital is locked. ( ABC News: Samuel Yang )

George Edmund Hampel is the sole director and secretary of firms trading under the names Cooper & Oxley Builders and Cooper & Oxley Builders WA, according to records filed with the Australian Securities and Investments Commission.

A firm registered at Mr Hampel's residential address, Ozena Nominees, is the sole shareholder of both private, unlisted businesses.

Cooper & Oxley Builders had multiple directors in the early 1990s, but four stepped down on the same day, just under five months after they were appointed.

William Rivett was left as the sole director.

Mr Hampel was appointed about a month later, and Barry Edwards about four months after that.

Mr Edwards stepped down in 2011, and Mr Rivett in 2013.

Financial records are not available for Cooper & Oxley Builders, but Cooper & Oxley Builders WA filed an audited financial statement on December 19.

It was set up as a holding company for a building and construction business operated via a unit trust.

It posted a loss for the 2016/17 financial year of $614,621.

It wrote down $614,621 in assets, while in 2015, listed $14.8 million of write downs.

In a signed declaration, Mr Hampel said it was his opinion there were reasonable grounds to believe the firm would be able to pay its debts when they fell due.