Australian authorities have issued heatwave warnings across most of the country as millions celebrate Australia Day on 26 January. Temperatures could peak in the 'high forties' Celsius in Victoria and South Australia on Tuesday, according to the Bureau of Meteorology. South Australia already reached 48.5C on Sunday, triggering warnings of fire danger. Some national day events, like Adelaide's parade and light show, were cancelled for safety. Organisers said, "While this is deeply disappointing for the community, performers and partners, community safety and wellbeing must come first." Heatwave alerts also cover New South Wales, Queensland, Tasmania, Northern Territory, and the Australian Capital Territory, lasting until Wednesday. Victoria's emergency management commissioner Tim Wiebusch told ABC, "We haven't seen heatwave conditions like this in Victoria for almost 20 years... this is a very serious set of weather conditions." The Bureau warned of "extreme fire dangers" in parts of South Australia and south-west Victoria due to hot, dry weather and gusty winds. Firefighters in Victoria are battling several blazes that have caused evacuations and threatened homes. The heat is affecting the Australian Open too. Tennis player Jannik Sinner suffered cramps on court, and play paused as nearly 80,000 fans were advised to stay safe in the heat. Meanwhile, Western Australia faced Tropical Cyclone Luana over the weekend, damaging homes and a beach resort before weakening inland. The meteorology bureau advised people to cool down by staying indoors, closing windows, and drawing curtains.