A thunderstorm asthma warning has been issued for much of Victoria's east.

People in central, west and south Gippsland have been warned there is a high risk of developing the condition due to a combination of high grass pollen levels, thunderstorms and strong winds.

There is a chance a large number of people may develop asthma symptoms over a short period of time, the state's health department says.

A moderate risk warning is in place for the Mallee, Wimmera, southwest, north central, northern country, northeast and east Gippsland.

People have been told to avoid being outdoors in a storm or during winds before a storm, take preventative medication and carry a reliever.

Health authorities earlier warned of a heightened risk of thunderstorm asthma, and that peak season for the condition could run until January due to a longer than usual grass pollen season.

Ambulance Victoria emergency management director Justin Dunlop also warned conditions are similar to 2016, when ten people died and emergency departments were overwhelmed during a thunderstorm asthma event.

Among those affected by the epidemic were people with seasonal hay fever who had not ever had asthma.