The ACT Health Directorate is warning Canberrans, especially those with asthma and hayfever, to take extra precautions on Sunday and Monday as potentially severe thunderstorms roll in.

The thunderstorm-induced asthma happens when high grass pollen levels combine with strong winds from thunderstorms and can cause severe asthmatic reactions from some people.

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"Not all thunderstorms produce an asthma event, and thunderstorm asthma is a rare event. However, people who suffer from hay fever and/or asthma are encouraged to be vigilant over the next two days for any worsening of their condition," the directorate said.

"Where possible, avoid being outside during a thunderstorm - especially in the wind gusts that come before the storm. Go inside and close your doors and windows. If you have your air-conditioning on, turn it onto recirculate."

The asthma events can lead to severe symptoms and have previously been linked to a number of deaths.

ACT Health urges anyone experiencing severe symptoms not relieved by usual treatments to seek urgent medical advice or call 000 in an emergency.