Construction on a major road project is set to grind to a halt for days after the discovery of a sinkhole.
One of the tunnel boring machines on Melbourne's $26.1 billion North East Link project was moving towards Lower Plenty Rd on Thursday night when the discovery was made.
No workers were injured but works in the area were immediately suspended.
A sinkhole is a void in the ground caused by a collapse in the surface layer.
It typically occurs when earth such as limestone and gypsum has no natural surface drainage and instead drains downward into sub-surface layers.
Transport Infrastructure Minister Gabrielle Williams said the sinkhole opened up at an old army barracks site and was about one metre wide and 18m deep.
The machines are digging twin 6.5km tunnels between the suburbs of Watsonia and Bulleen in the city's northeast.
One has paused and the other underneath the sinkhole is being moved to a safe zone.
Crews are laying out concrete rings to secure the ground so engineers can investigate the cause, Ms Williams said.
There was no risk to the community or property, and she was hopeful work would resume in the coming days.
"The site is safe," Ms Williams told reporters on Friday.
"WorkSafe were on the site last night, the engineers were on the site last night and they'll continue with an abundance of caution."
Victorian Opposition Leader Brad Battin said it was yet another "big black hole" on a major project, referring to budget blowouts on several state government transport initiatives.
"The government need to explain to the community exactly the cost this is going to (have) on that project," he said.
"Is it going to impact the timeline?"
The machines are meant to dig up to 15m per day and up to 45m underground ahead of the road's scheduled opening in 2028.
Cost estimates for the project have grown from $10 billion in 2016 to $15.8 billion in the 2017 business case and $26.1 billion in December 2023.
The Albanese government came to its rescue with an extra $3.25 billion in the 2024 federal budget, lifting its total contribution to $5 billion.
