Four people have been evacuated after 100 litres of nitrous acid leaked from a gas tank inside a Thomastown factory.
Emergency services are working to contain the chemical leak at a factory on Holt Parade, Thomastown, which began around 10.15am.
Firefighters in breathing apparatuses entered the building to rescue four workers, who are being assessed by Ambulance Victoria on the scene.
No one has been injured.
An exclusion zone of 250m has been established around the factory, and people have been advised to avoid the area.
Fire crews continue to work to neutralise the spill, which could take several more hours, Metropolitan Fire Brigade (MFB) said in an official statement.