Twenty-five people have been evacuated over a major gas leak in Melbourne's southeast that has closed several streets.
Fire crews in protective gear are applying water spray to safely disperse the gas cloud and prevent an explosion at the Valley Street site in Oakleigh South.
The earthmoving equipment ruptured the gas main just before 8am on Tuesday, the Metropolitan Fire Brigade said.
Commander Ron Young said workers digging a trench broke a 50mm high pressure line, causing the leak.
"There's no issue and no threat to residents at the moment even though residents have been evacuated," Mr Young said.
"Our hazmat crews are monitoring the atmosphere and the readings are quite acceptable and there's no dangers."
Mr Young said the local gas authority has located the valve and is trying to turn it off to stop the leak.
"If they can get the valve off it'll take five minutes, but if they can't get the valve to turn off, they'll have to dig it up and clamp it which could take a few hours," he said.
A Community Advice notice has been issued due to the danger of possible explosion and police and paramedics are on stand-by.
Specialised air monitoring equipment and operators are also responding.
No injuries have been reported.