Hundreds of tradies have been booted off worksites across the country over fears construction firm Probuild is on the verge of collapse.

Subcontractors and tradesmen walked off the site this afternoon, including on Melbourne's O'Connell Street, where Probuild is behind a build for biotech giant CSL.

Workers were seen loading large amount of equipment and tools from Probuild building sites.

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Probuild's portfolio of ongoing work across Australia estimated to be valued at $5 billion and includes Greenland Centre, Sydney's tallest residential building.

The company is expected to make an announcement about its future tomorrow morning.

Long building delays and company not having enough money to pay its subcontractors are believed to be the factors behind Probuild's expected collapse.

A tradesman who fled one of the building sites told 9News: "All the contractors are owed hundreds of thousands of dollars.

"No one's going to get their money," he said.

More to come.