MELBOURNE - An intense heatwave swept southern Australia on Wednesday, with temperatures in multiple locations soaring above 40 degrees Celsius.

In downtown Melbourne, the mercury rose to 42 degrees Celsius on Wednesday afternoon, making it the hottest day since January 2020.

People flocked to the beaches to seek a touch of coolness while Ambulance Victoria said they had experienced a 12-percent increase in workload on Wednesday.

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Ambulance Victoria reminded the public to keep hydrated, avoid going out during the hottest part of the day, and use air conditioning and fans if necessary.

Meanwhile, residents of Bungil, Granya and Thologolong, small towns over 280 km northeast of Melbourne, have been ordered to evacuate or take shelter due to the threat posed by nearby bushfires.

An alert issued through the VicEmergency service said that a fire to the east of the three towns is out of control and could impact properties.

"Leaving immediately is the safest option, before conditions become too dangerous. Emergency services may not be able to help you if you decide to stay," the warning said.

Chris Hardman from Forest Fire Management Victoria said at a press conference on Wednesday afternoon that over 300 firefighters and around 12 aircraft were working to contain the fire, which has burned through about 1,000 hectares of land.

A separate warning for the towns of Longwood, Longwood East, Ruffy, Tarcombe and Upton Hill, around 120 km north of Melbourne, said that a bushfire in Longwood is moving southeast and that it is too late to safely leave the area.

Residents in the area have been advised to immediately take shelter in a room that has two exits and close all exterior doors, windows and vents.

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"You must take shelter before the fire arrives. The extreme heat is likely to kill you well before the flames reach you," the warning said.

Jason Heffernan from the Country Fire Authority said on Wednesday that authorities expect fire conditions to be at the "upper end of extreme" across Victoria on Friday when temperatures are again forecast to reach 40 degrees Celsius.

It will be the worst heatwave since the disastrous Black Summer bushfire season in 2019-20 when an estimated 1 billion animals were killed and 33 people directly died of the fires.