Australia is enduring its worst heatwave since 2019-20. Victoria’s Hume Highway has closed. Regional trains and buses are cancelled in fire risk zones. Firefighters from at least two states are fighting severe blazes. Melbourne expects a scorching 41C on Friday. Acting Premier Ben Carroll called Victoria "one of the most bushfire-prone areas in the world". He warned of "the real risk of heat-related illness throughout the state tomorrow". The state health department urged people to stay hydrated, indoors, and check on loved ones. Fire danger will be catastrophic in multiple Victorian areas including south-west, Wimmera, and northern districts. Fires burn now near Longwood and Walwa, where residents must "leave immediately". The Bureau of Meteorology reports extreme heat warnings for every state and territory except Queensland. Highest temperatures by Thursday afternoon included 45.8C at Hopetoun airport (Victoria), 44.9C at Tarcoola (SA), 43.7C at Paraburdoo (WA), and 43C at Hay (NSW). Adelaide hit 43C on Wednesday and woke up to 31C Thursday. BoM meteorologist Sarah Scully said, "The heat is intensifying right across southern Australia." Hot conditions are expected in Canberra and New South Wales from Friday. Sydney's central areas were to reach 33C Thursday, with some western suburbs hitting 40C. Catastrophic fire ratings have not been seen since 21 November 2019, said Victoria’s emergency management commissioner Tim Wiebusch, recalling devastating 2019-20 fires. "Catastrophic fire danger ratings mean that it will be unpredictable, uncontrollable, and fast-moving fires that we will see tomorrow." The entire state of Victoria will be under a total fire ban Friday. The Hume Freeway is closed both ways between Seymour and Violet Town. Freight and regional V/line services are cancelled in high-risk districts. Public lands and parks are also closed. Storms with hail and dry lightning may worsen fire risks in Victoria and southern NSW. Animals at Sydney's Taronga zoo are given ways to cool, such as "blood-sicles" ice treats for lions, said Brendan Host, behavioural husbandry supervisor. Native wildlife suffers too; hundreds of flying fox pups have died from heat in South Australia. Wildlife experts advise leaving fresh water in shady spots to help. Many places in Victoria recorded their hottest day since 2020, with Melbourne reaching 40.9C and Avalon airport near Geelong hitting 43.6C. Coastal towns in Western Australia came close to 50C. The climate crisis fuels extreme weather events. University of Melbourne climate scientist A/prof Dr Andrew King said, "Our emissions are causing worsening heatwaves and fire weather in particular. The longer we delay real action to greatly reduce our greenhouse gas emissions, we can expect even more intense heatwaves and fire weather for years to come."