Professor Mike Roberts, a leading respiratory specialist with Victoria's Department of Health, has forecast a high-risk of epidemic thunderstorm asthma in the state's central weather district on Thursday.

The Mallee, North Central, North East, Northern Country, South West, West and South Gippsland and Wimmera districts are deemed to have a moderate risk.

The mercury reached 33C in Melbourne at 1.34pm on Thursday but severe thunderstorm activity and strong winds are tipped to hit parts of the state later in the day.

Combined with forecast high grass pollen levels, the health department said there is a "significant risk that people with asthma, hayfever and nasal allergy (seasonal rhinitis) may develop significant symptoms immediately before and during the storm period".

It recommends people avoid wind gusts before the storm, go inside and close windows and doors.

A thunderstorm asthma event in Melbourne in 2016 killed at least nine people and resulted in thousands more in hospital.

It comes as an annual report shows the hours spent by emergency service workers attending to storm call-outs spiked 170 per cent after a busy year of major weather events.

Victoria's State Emergency Service has revealed 2020-21 was its second-busiest year on record as its members responded to 36,396 calls, 84 per cent of which related to floods and storms.

The number of flood incidents (2181) was stable year-on-year but those linked to storms jumped from 24,926 to 28,341, a 13.7 per cent rise.

The more dramatic rise came in the time SES workers spent on the ground cleaning up, providing relief and other early recovery support from storms.

While accounting for 150,748 SES staff hours in 2019-20, that figure grew to 408,139 in 2020-21 - a 170 per cent rise.

The VICSES annual report, tabled in Victorian parliament on Thursday, notes 10,000 calls for help were made over three days in June after storms and floods ripped through parts of the state.

The wild storms hit Gippsland and the Dandenongs on June 9 and 10, killing two people, damaging the Yallourn power station and leaving more than 320,000 people without power.

It was the largest event in the service's history.

Other major events over the 12-month span included damaging winds in late August which left 150,000 Victorian properties without power, the Horsham tornado on December 7 and statewide storms and floods in early January.

Australian Associated Press