Sydney: Four people died and thousands more Australians were left gasping for breath following Melbourne’s “thunderstorm asthma”, with the state’s health minister saying on Wednesday that it was lucky there were not more.

The rare condition is created when heavy rain and winds whip up extremely high pollen levels.

Hospitals were swamped with emergency patients, while firefighters and police were called on to help paramedics respond to thousands of calls after the conditions caused breathing problems for Victorians.

Jill Hennessy, the Health Minister, said it was like “a bomb going off”, with all ambulances, police, fire and non-emergency transport being used to deal with the crisis.

“Our health system was stretched to the limit,” she told 774 ABC Melbourne.

“We know that we’ve got some people in intensive care units as well.

“At one point we had 140 code one cases, while dealing with other patients, all of them were cardiac arrests or severe respiratory conditions.”

The unusual phenomenon happened after an evening storm in Melbourne churned up pollen and dust from parkland and bushland around the city. “Thunderstorm asthma” causes severe breathing issues and can affect those with hay fever and pollen allergies as well as asthmatics.

The incident prompted a “major disaster response” as emergency services received about 2,000 calls for help. David McGann, 35, said his asthma was “three to four times worse than I’ve ever felt”. He told ABC News: “I couldn’t get off the couch for three hours last night just due to shortness of breath … it felt like an elephant had his foot on my chest.”

Two people died while waiting for ambulances and about 30 people were treated in intensive care. Some patients said they had had no asthma issues since childhood.

Pharmacists were inundated by requests for Ventolin inhalers and the ambulance service was at full stretch. Hope Carnevali, 20, a law student, died in her front garden after a 30-minute wait for an ambulance. Omar Moujalled, 18, died at a GP’s surgery.

Apollo Papadopoulos, 35, and Clarence Leo are the latest men confirmed to have died due to an asthma attack. Dr Tom Connell, from Melbourne’s Royal Children’s Hospital, said: “Just the sheer number of patients; it is unprecedented in our history.” Previous outbreaks of “thunderstorm asthma” have been reported in London, Birmingham and Naples.

In Melbourne, the condition typically occurs alongside a spring storm with a sudden change in humidity and strong winds that cause rye grass pollen capsules to explode into tiny particles which are then inhaled. The phenomenon was not formally identified until 1992 but Melbourne has had occurrences in 1987, 1989 and 2011.

A number of reviews were launched into Monday night’s emergency, including by the State Government.