The smoke blowing in from the deadly bushfires still raging in East Gippsland caused the second day of poor air quality for the city, with the closure of a runway at Melbourne Airport and some flights delayed.

But the weather front that brought heavy rain to Melbourne late on Wednesday could mean more bushfire trouble.

The thunderstorm carried lightning that ignited fires in the Great Otway National Park and as the front moves across the state, authorities fear it could do the same in the fire-ravaged East Gippsland and northeast regions.

Ambulance Victoria received more than 100 calls during the morning from people with breathing problems, an increase of 75 per cent.

The cool change swept through Melbourne mid-afternoon and the temperature plummeted from the mid-30s to the low 20s.

While the storms cleared the smoke, there were warnings of flash flooding in Melbourne.

The Bureau of Meteorology issued a severe thunderstorm warning for many parts of the state, along with Melbourne.

The thunderstorm is expected to clear overnight in Melbourne, with a shower or two forecast for Thursday.

By 6pm on Wednesday, six 'Watch and Act' alerts remained in place for the fires that have devastated East Gippsland since November 21.

The death toll from the fires rose to five on Wednesday, after authorities confirmed the November 30 death of Forest Fires Management contractor David Moresi, 69, near Gelantipy would be added to it.

"David was a pillar of the community, a dedicated educator. He loved the bush and he inspired so many people to be in the great outdoors," Chief Fire Officer of Forest Fire Management Victoria Chris Hardman said.

Mr Moresi is survived by his wife, Judi, three children and many grandchildren - "the great bushmen of the future" whom he taught to shoot, fish and hunt.

The Australian Defence Force, meanwhile, was involved in clearing fallen and badly burnt trees from across the Princes Highway - the main road between the East Gippsland and the NSW South Coast.

This road is also the only road out of Mallacoota, the town that became isolated in December.

More than 1500 people were evacuated from Mallacoota on military vessels and aircraft after it was suddenly cut off by bushfires and people sheltered on the beach more than two weeks ago.

It's Australia's largest peacetime humanitarian rescue mission since Cyclone Tracy and more have since left by a road convoy.

This traumatic experience was relived by a small group of residents in a town cut-off by fire on Wednesday night.

The around 12 people that remained at Tamboon were forced to shelter on the beach after a blaze in Victoria's East Gippsland flared.

There are 1500 firefighters battling the blazes, including 130 from overseas and another 140 international personnel will arrive later in January.

Australian Associated Press