The thunderstorm asthma risk has been raised to moderate in parts of Victoria and people should prepare in case one strikes.
Vic Emergency warned on Sunday of "a moderate risk for epidemic thunderstorm asthma" over the next three days in the North Central, Northern Country and Central forecast districts, which includes Melbourne.
A Department of Health and Human Services spokesman said moderate was in the "plan and prepare stage" of the early-warning system and there was no immediate danger.
"The forecasting system takes a cautious approach and forecasters may predict such conditions more often than they occur," Vic Emergency says.
People in affected areas should check the thunderstorm warning app or Vic Emergency for updates in case the situation changes and have their asthma plan ready.
A thunderstorm asthma warning system was introduced in the state last Monday after nine people died and thousands suffered respiratory symptoms in November 2016 as a result of what experts say was the world's worst recorded asthma thunderstorm.
The monitoring and alert system will warn people about the risk of thunderstorm asthma three days before an event is expected and will run from October to December every year, which is during the grass pollen season.
It predicts the risk of thunderstorm asthma by analysing grass pollen forecasts, weather observations and data such as temperature, wind changes, rainfall and grass coverage.
A traffic-light scale will then identify the risk as low, moderate or high.