Forecasts of high grass pollen levels and thunderstorms with strong winds in the Central, Westand South Gippsland districts have sparked the warning from the state's Chief Health Officer Dr Clare Looker.
Hay fever and asthma sufferers have been urged to take adequate precautions and remain vigilant.
There is a moderate risk of thunderstorm asthma in place for the Mallee, Wimmera, South West, North Central, Northern Country, North East and East Gippsland districts.
Wild weather lashes Melbourne
Thunder, lighting and heavy rain inundated the city with water, following flash flooding overnight.
A driver was even stuck in floodwaters at the Dudley Street underpass in Docklands.
There's a chance of thunderstorms could develop this morning across Melbourne, bringing strong winds and rain.
Affected people are urged to take preventative medication as directed and follow an asthma action plan, even if symptom-free.
The forecasting system enables people who have asthma or seasonal hay fever – and who are at risk – to plan ahead and reduce their risk.
Call Nurse on Call on 1300 60 60 24 or see your local doctor if you require medical advice.
Call triple zero immediately if someone is not breathing, if their asthma suddenly becomes worse or is not improving, or if the person is having an asthma attack and a reliever puffer is not available.
