"Our fingers are crossed that this continues over the coming days," the New South Wales Rural Fire Service (RFS) said Friday in a tweet.
Rain has fallen on most firegrounds in the state over the last 24 hours, the RFS said. However, it wasn't enough to put out the flames. Eighty-two fires are still burning, including 30 that are yet to be contained.
Residents of drought-hit areas who have spent years waiting for rain celebrated its arrival on Thursday. Rain fell in major cities, including Sydney, where water flowed through the streets.
Forecasters predict more rain over the next few days, but they warn it could cause flash flooding in areas of parched land. Years of drought have left some regions so dry that rain just runs off the ground. The massive fires have burned through some of the vegetation that would normally soak up the precipitation.
Trees weakened by fire are also at risk of falling, and rain could wash ash and debris in waterways, causing water pollution, authorities say.
The Victoria State Emergency Service posted several images on Facebook showing damage from the storm, including a sinkhole four meters (13 feet) deep.
Lightning from the storms has sparked a number of new grass fires in New South Wales and Victoria, though it's hoped the damp conditions will help stop the flames from spreading.
Parts of Melbourne were hit with as much as 77 millimeters (3 inches) of rain, causing flooding and some damage, the Victoria Bureau of Meteorology said Thursday.
Earlier this week, the New South Wales RFS had said that if the rain forecasts held true, it could be a panacea for the region's firefighters.
At least 28 people have died nationwide, and in the state of NSW alone, more than 3,000 homes have been destroyed or damaged. State and federal authorities are struggling to contain the massive blazes, even with firefighting assistance from other countries, including the United States.
Smoke from the fires has blanketed major cities in haze in recent weeks.
Rain has helped clear the skies, but the air quality is expected to worsen in coming days, according to the Victoria Environment Protection Authority.
Tennis Australia officials say they're taking precautions to protect players should the heat and smog return.
Temperatures in Melbourne have dropped sharply in the last 48 hours, to below 20 degrees Celsius (68 Fahrenheit), eliminating the risk of excessive heat -- for now.
CNN's Jessie Yeung contributed to this report