Although it has recently been affected by bushfires, many places have a fire ban, so many cities have canceled their fireworks displays. However, according to the Southbank Offical website, there will be a ten minutes long firework display on 26th Jan(Australian Day) at 7.30pm. The best places to watch are the Clem Jones Promenade and the Cultural Forecourt. Also, there are various Australian day celebrations in Southbank during the day time. You can refer to their official website
