Workers evacuated after nitrous acid spill

Four workers have been rescued from a Melbourne factory following a nitrous acid leak that resulted in an orange cloud forming in the city's north.

MFB crews in breathing apparatus helped move out the employees on Saturday morning after they'd taken shelter in a protected area of the building.

About 100 litres leaked from the tank with MFB crews now working to transfer the rest of the contents of the 1000 litre tank into a clean container.

Ambulance Victoria assessed the four rescued workers who weren't contaminated and didn't require any emergency treatment.

A 250-metre exclusion zone was earlier created downwind of the tank which had been "off gassing" which caused the orange cloud.