Victoria has recorded the worst air quality in the world as thick smoke wreaks havoc with people's health and hampers medical efforts in fire-affected areas.
Thick smoke stretched from fire-ravaged Gippsland, past Melbourne to Geelong, with hazardous air quality across most of the state on Tuesday.
"Overnight for Melbourne it did reach the worst in the world," the state's Chief Health Officer Brett Sutton said.
Vulnerable groups like children, the elderly and those with pre-existing conditions should stay inside, he added.
Royal Melbourne Hospital respiratory medicine head Lou Irving said smoke from the fire grounds would pick up additional pollutants as it drifted.
"Although it started as wood fire smoke, it actually picks up other particles along the way and in Melbourne you can have diesel and pollens attaches to it - it's a mixed bag - potentially more irritable than pure wood fires," Associate Professor Irving said.
For those on the fire ground for 60 days or more, it's possible they may develop chronic bronchitis, he added.
Mallacoota-based doctor April Armstrong said the smoke on Tuesday was some of the worst since the fires hit.
"Now with the wind change we are getting the smoke back in. We are still getting fires here. Not just new smoke but old smoke too," she told AAP.
Dr Armstrong is coordinating a team working around-the-clock at Mallacoota Medical Centre, as local doctors keep an eye on unstable patients in the Victorian town.
The smoke in Sale has hampered aircraft taking off with medical supplies to land in Mallacoota, she said.
A bus, with a police guard, is on the road to Merimbula Airport to get volunteers out and supplies in, she said.
"More staff come in and out all the time. We are pretty good we have not run out of anything," she said.
But with five times as many patients for the month, supplies of hand towels and sanitiser are getting low.
Blood and skin samples still need to get out too, she added.
There are 16 fires going in Victoria and 1.4 million hectares burnt, killing four men and destroying 353 homes and 548 other structures.
Smoke from those fires and blazes in NSW has created terrible air quality across much of the state, setting off fire alarms and delaying parts of the Australian Open.
More than 110 breathing-relating calls were made to Ambulance Victoria between midnight to 11am, while metropolitan firefighters responded to 220 false alarms since 10pm Monday.
One of the four men killed in Victoria's fires, Mat Kavanagh, was farewelled on Tuesday in a funeral at Alexandra.
A guard of honour was formed on the main street in Alexandra as the hearse drove past carrying the 43-year-old Forest Fires Management worker who died in a crash on his way to the fires. A driver has been charged.