Residents of Victoria's Wimmera region have been warned of a severe risk of thunderstorm asthma with conditions across the state right for a widespread outbreak.
The combination of high levels of pollen and a high likelihood of thunderstorm activity has prompted health authorities to warn people to prepare ahead of this afternoon's forecast storm.
Deputy chief health officer Angie Bone said Victorians should make sure they have medication at hand.
"If a storm arises, the best thing to do is go inside, shut the doors and windows, turn off the air-conditioner so you don't let any pollen into the house," Dr Bone said.
Dr Bone said the main risk was focused on the Wimmera but other regions could suffer.
"The risk in Melbourne is forecast to be moderate. I would say that none of this is an exact science these are only forecasts," she said.
In November 2016, Melbourne suffered the world's largest outbreak of thunderstorm asthma, with thousands of people presenting to hospital with breathing difficulties.
Chief executive of Asthma Australia Michele Goldman said the conditions were right for a similar event.
"It's a perfect storm, having high levels of grass pollen and the likelihood of a thunderstorm," she said.
Ms Goldman said even people who have never experienced asthma should be aware of the conditions.
"The pollen don't get trapped in our upper airways, it travels down into our lower airways where it can cause asthma, even for people who may not have had asthma previously," she said.
