A major storm that hit Melbourne on Monday night appears to have caused a mass outbreak of an illness known as “thunderstorm asthma”.

The Age reports that an unprecedented number of people fell acutely ill on Monday after the storm struck at around 6pm.

Two people in Melbourne’s west died, including a man waiting 30 minutes for an ambulance.

Other emergency services helped respond to the unexpected demand and hospitals were also overwhelmed as people presented at emergency departments with respiratory problems.

Thunderstorm asthma occurs when wind and moisture cause pollen to rupture into small particles that can be inhaled, rather than being filtered out by the nose, causing an asthma attack.

The smaller particles mean it can induce an asthma attack in people who have never had symptoms before. Symptoms include shortness of breath, chest tightness, coughing and wheezing. Anyone with a rye grass allergy is highly susceptible to the illness.

(There’s more details on how it happens are here.)

The ABC reports that some hospitals and pharmacies ran out of Ventolin puffers and St Vincent’s Hospital, in Fitzroy, enacted its “code brown” procedure for the first time in five years in a bit to free up beds.

Victoria SES volunteers responded to more than 130 requests for assistance due to damaged buildings and downed trees last night, especially in the Hobsons Bay and Wyndham regions in the city’s west.

Ambulance Victoria @AmbulanceVic

High demand for ambulance for breathing issues due to weather. Only call 000 in an emergency & consider other options for minor complaints

6:08 AM - 21 Nov 2016

Ambulance Victoria executive director emergency operations Mick Stephenson said it was an “unprecedented workload” after the severe storm hit at 6pm following the hottest day since March.

“Between about 6 o’clock and 11 o’clock we responded to in excess of 1870 cases, which is six times the workload for that period of the day,” he said.

“Most of those cases were respiratory-related.”

Stephenson said the service turned out 60 extra ambulances, and converted all non-emergency ambulances to emergency ones, as well as getting police and firefighters to assist with checking on patients.

Around 200 people called and said they had asthma specifically, while another 600 reported breathing problems.

“What we do know is there are a lot of people who called last night who’ve never had asthma before, so this is their first experience,” he said.

A very high pollen count yesterday evening was exacerbated by when the storm hit.

“When the storm swept through, pollen levels rose dramatically,” Stephenson said.

“And there were many people who didn’t know they had asthma who developed asthma for the first time last night as a consequence of the pollen.”

He said incidents of thunderstorm asthma were rare and and the last incident to happen in Melbourne occurred in 2010

The cardiac arrest rate rose also last night.

“We don’t know if those deaths are related to this particular incident. We will review those,” Stephenson said.

He said it was a “full scale event”.

“It’s as busy as we’ll be and as much escalation as we’ll every do.”

Victoria Health has issued a guide to dealing with asthma.