The entire state of South Australia was without power Wednesday after being pummelled by a severe storm, with the blackout causing chaos as authorities warned of more wild weather.The state -- about one and a half times the size of France and with a population of some 1.7 million -- lost power after severe thunderstorms struck with destructive wind gusts of up to 140 km per hour (87 mph), torrential rain and large hailstones.Trees were torn down, roofs ripped out, thousands of homes and business were without power and cars were gridlocked on flooded roads as traffic lights stopped working in what the Bureau of Meteorology said was one of the most intense storms to hit the state in recent years.South Australia's Premier Jay Weatherill told local ABC radio the duration of the outage was "unknown". He called on people to avoid travel as authorities sought to restore the network "in the coming hours"."At this stage we're still gathering information about the cause, but it appears that there was a weather event which has damaged infrastructure in the Port Augusta region," Weatherill said, adding that the grid had shut down to protect itself after a "dramatic drop in frequency" in the power network.SA Power Networks, which runs the state's electricity distribution network, tweeted that South Australians should "brace for extended outages and ensure you conserve mobile device battery"."We're experiencing a statewide outage and have no supply from the upstream transmission network," it added.The stormy conditions were forecast continue through Thursday.Federal Energy Minister Josh Frydenberg told Sky News "serious questions" would be raised about how a major state's entire electricity supply could be knocked out by severe weather.