Severe thunderstorms hammered northern NSW and southeast Queensland on Monday, dropping giant baseball-sized hail in the worst-affected areas.
The Insurance Council of Australia received more than 16,000 claims across more than 140 postcodes on Tuesday, with the damage bill yet to be tallied.
Declaring the event a catastrophe enables insurers to streamline the response and direct urgent assistance to the worst-impacted property owners.
"While it's too early to estimate the insurance damage bill, we expect to see claims numbers continue to rise over the coming days as power returns to homes," Insurance Council's Kylie Macfarlane said.
"This event comes off the back of recent widespread rainfall and storm activity across similarly impacted regions, and insurers are focused on processing claims from these events as quickly as possible."
Emergency crews have worked through heatwave conditions to restore power ahead of another round of dangerous superstorms.
Giant hail and cyclonic winds swept Queensland's southeast on Monday, leaving a wild trail of destruction that damaged homes, shut down public transport and closed schools.
More than 162,000 properties were left at one stage without power, with extra crews called in from across the region to help.
About 95,000 were still to be restored on Tuesday morning, amid warnings some areas may not have power restored for another 24 hours.
Thousands of properties remained without power on Tuesday afternoon.
"There were more than 600 powerlines down, and Energex counted more than 880,000 lightning strikes during the storms," an Energex spokesman said.
At least two homes lost their roof in the wild weather, with more than 2200 urgent calls to emergency services during the storm's peak.
"We did see hail of 11 to 12cm in diameter at places like Manly (in Brisbane's east)," Bureau of Meteorology's Jonathan How said.
Thousands of commuters were affected as trees and power lines were brought down, bringing the rail network to a halt.
Disruptions continued on Tuesday, with major rail delays and 11 schools closed for storm repair, while repair work resumed in high humidity with more storms on the way.
Large parts of Queensland are sweltering in heatwave conditions, with temperatures set to soar across much of the state in the week ahead.
Gold Coast, Brisbane, Sunshine Coast and Wide Bay are set to endure "very unstable conditions" on Tuesday, amid four consecutive days of severe thunderstorms forecast for the state's southeast.
The bureau warned on Tuesday communities already impacted by storms may be placed under additional stress by further power outages, travel delays and potential damage to infrastructure.
17°C