A fourth death has been attributed to Melbourne's "thunderstorm asthma" emergency on Monday night, and it was lucky there were not more according to the state's Health Minister.

More than 2,000 people suffered breathing problems when a severe storm combined with an extreme pollen count to cause what is being described as "thunderstorm asthma".

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."

Student died two days before graduating from high school

Apollo Papadopoulos, 35, and Clarence Leo are the latest men confirmed to have died due to an asthma attack.

Meanwhile friends and family have been paying tribute to the two other victims, Omar Moujalled and Hope Carnevali.

Mr Moujalled, 18, was a student at the Australian International Academy at Coburg North, in Melbourne's inner north.

"It is with great sadness and a heavy heart that we inform you of the death of Omar Moujalled, one of our Year 12 students. Sadly, he passed away last night from a medical condition," a statement on the school's Facebook page read.

"Omar was an exemplary student, role model and principled, who was previously part of the captaincy team and a much-loved, respected student."

Friends and family donated to a crowdfunding campaign to build a well in his honour.

"On the 21st of November 2016, a friend, brother, son and classmate was lost to a tragic asthma attack at the age of 18," wrote Sarah Baarini, who set up the campaign.

'My heart breaks for your family'

The ABC understands the second victim was Hope Carnevali, a 20-year-old law student.

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Ms Carnevali's relatives told 7 News Melbourne it took more than 40 minutes for an ambulance to arrive.

"Just knowing that, if they had of gotten there a little earlier, that the situation might be different, is very hard to deal with," Hope's aunt Melissa Carnevali said.

Friends have posted tributes on Facebook and started a crowdfunding campaign to assist with funeral costs.

"My heart breaks for your whole family. You had been through so much and always managed to have a smile on your face. I will never forget you. Rest in peace," Michelle Anne Haber wrote in a post on Ms Carnevali's Facebook page.

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

Ms Hennessy said the Government would also examine the overall response to the event to ensure the state can cope with similar incidents in the future.