Sebastopol resident Everall lives near the Royal Mail and heard the loud whooshing sound, comparable to that of a jet engine.
Initially he thought that construction workers were simply using heavy machinery, until he heard sirens and wandered down the street to see three fire trucks, Lucas Hazmat and police cars.
Brigades at the scene include Sebastopol, Lucas and Ballarat City.
Contractors had been working on an excavator at the site, digging around a water pipe, when they hit the gas line.
Hearing the initial roaring sound of gas escaping, the contractor realised they had hit the gas line and immediately called 000. Nobody was injured.
Senior Station Officer Wayne Martin, from Ballarat City Fire Brigade, said the contractor had been following the plans, but the gas line was not where it was not marked on the map.
It is understood the gas main has a diameter of 50 metres.
The gas company is currently at the scene to cut off and isolate the gas leak. There are three spots it must be isolated.
Firefighters have conducted atmospheric monitoring and have deemed it safe for cars to pass through the outbound lane, but a chemical hazard warning remains in place.
A pungent gas smell can still be smelled in the air and community members are urged to avoid the area.
There is currently no threat to the community.
A firefighter is located on the median strip, pointing a hose at the source of the leak in case it ignites.
Firefighters will remain at the scene for several hours until the leak is isolated and the area deemed safe.
Residents in Sebastopol and Magpie have been warned that hazardous gas is leaking into the air this morning.
The CFA has issued an advice warning for people towards the southern end of Sebastopol.
The leak originated near the Royal Mail Hotel, where an excavator appears to have ruptured a line under the road.
Inbound traffic has been blocked to vehicles.
The leak is making a loud noise and can be heard more than 100 metres away.
One person at the scene told The Courier it sounded like a "jet engine".
The warning zone covers a large area, stretching from Dowcra Street, right up to Marty Busch Reserve.
Crews were first called just after 9am.
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