Work has again been halted on the West Gate Tunnel project, this time after what has been described as a minor underground collapse in Melbourne's inner west.
The Australian Workers' Union has confirmed no one was hurt when part of a cross passage between the twin tunnels collapsed in the early hours of Friday.
The union's construction organiser, Joel Archer, said it happened about 1 kilometre in from the tunnel entrance at Yarraville and between 300 metres and 500 metres underground.
"During excavation of one of the cross passages in the West Gate Tunnel project, there was basically a collapse from unstable ground," Mr Archer said.
"There's a high moisture content. Basically, it's not even considered solid ground."
Mr Archer said none of the workers were hurt and crews were immediately evacuated from the tunnels.
"It's not considered catastrophic but what has happened is works have ceased."
Workers to remain off site until ground can be stabilised
An exclusion zone has been set up and geotechnical assessments have begun to determine what is needed to make the ground safe.
Mr Archer said work would not resume until that rectification work was completed.
"Works will remain stopped, people won't be allowed back down there until there's an engineering report," he said.
The union said it was not overly concerned by the collapse.
"Quite often around Melbourne, we're sort of sitting on a water table, so to speak," Mr Archer said.
"The public can be reassured that, as I said, no one was hurt and we've done everything we can to ensure that the workers are safe."
However, the Victorian division of the Construction, Forestry, Mining and Energy Union (CFMEU) accused the subcontractor responsible for the project, CPB Contractors, of "having a long history of safety breaches".
In a statement, the CFMEU described the incident as endangering workers as well as raising concerns about "further and more severe collapses within the tunnel".
CPB Contractors has been contacted for comment.
The project was meant to be finished by 2022 but work stopped when toxic soil was discovered, delaying completion by several years.
The tunnels are being built by toll road operator Transurban which referred the ABC to the state government for comment.
The government's Major Transport Infrastructure Authority confirmed there had been minor movement of rock and soil near the northern portal in Yarraville.
"The site has been secured and is safe. Works have paused and monitoring has been established," a spokesperson said.
WorkSafe has been notified about the incident and said inspectors were responding.
