While the Vic Emergency forecast for much of the region is low, a warning of moderate risk remains in place on Monday for the North Central forecast district, which encompasses Maryborough, Maldon and Castlemaine.

People at increased risk of thunderstorm asthma include those with asthma (or who have had asthma in the past) and people with spring hay fever.

Those at increased risk are advised to avoid being outside during thunderstorms and the wind gusts that come before a storm.

Doors and windows should be closed, and air conditioners should be set to recirculate.

Reliever medication should be available, those with asthma should ensure they have an action plan, and people should be alert to asthma symptoms.

People are also advised to learn the four steps of asthma first aid: sit the person upright; give four puffs of a blue or grey reliever puffer; wait four minutes, and if there is no improvement, repeat step two; and call 000 if there is still no improvement.

Thunderstorm asthma is thought to be triggered by a combination of high grass pollen levels and a certain type of storm.

The grass pollen grains can burst open and release tiny allergens that can be breathed deep into the lungs, triggering asthma symptoms.

Thunderstorm asthma events are uncommon, with only six reported in medical literature in Melbourne since 1980.

However, they can be deadly: a thunderstorm asthma event in Melbourne last November saw nine people die and thousands treated in hospital.

To access the thunderstorm asthma forecasts, download the Vic Emergency app or visit www.emergency.vic.gov.au/prepare.