A mechanical fault at a refrigeration warehouse on Army Road, Pakenham has been identified as the source of the leak.
Workers at the warehouse and residents from Timothy Close, Emily Close and Christopher Close have been evacuated to a nearby hall.
Appliances from Dandenong, Hallam, Nar Nar Goon and Pakenham are on scene, along with Dandenong’s Hazmat Detection vehicle.
The latest advice message for the incident is available on the CFA website: http://bit.ly/CFAmap.
Residents on Army Road are being advised to stay indoors with their windows and doors shut.
UPDATE from @VictoriaPolice:
The ammonia leak reported in Pakenham earlier today is now clear. Residents can return to their homes & road blocks will be removed by 12pm.