Giant hailstones bigger than 16cm (6.3 inches) appear to have fallen in Queensland, according to Australia's weather agency.
If confirmed, it's believed to be a new record for the country.
Forecaster Shane Kennedy, from the Australian Bureau of Meteorology, said the previous record was "around the 14cm mark".
"Hail that size has a terminal velocity of well over 100km (62mph) an hour," he told ABC News.
The bureau tweeted on Tuesday: "Giant hailstones in excess of 16 centimetres have been observed in Yalboroo, north of Mackay in Central Queensland."
Yalboroo is about 500 miles (804km) north of Brisbane.
Samantha Caporn - who lives in the area - posted a picture taken by her husband of three super-sized hailstones.
Hand-sized balls of hail and pictures of smashed windscreens were also posted on the Higgins Storm Chasing Facebook page.
Terri Shepheard posted a huge hailstone on the group's page - which she said she'd found two hours after the storm.
People caught up in the freak weather also reported shattered windows and damage to their vehicles.
Christopher Harvey, who was driving near Mackay, told ABC News the hail was bigger than his hand and that he had to pull over for safety.
"I took a quick video as it went through my back windscreen, then not long after it's gone through my front windscreen," he said.
"It hit my roof, pushed my glasses holder down, done a fair bit of damage."
A severe thunderstorm warning for parts of Queensland remains in place, with a forecast for "destructive winds, giant-sized hailstones and heavy rain".