Wild storms have caused the biggest blackout in South Australia since the entire state went dark in 2016. More than 423,000 lightning strikes were recorded on Sunday. Heavy winds downed trees and SA Power Networks received more than 500 reports of fallen wires. About 163,000 homes and businesses lost power as SA was cut off from the nation’s electricity grid after the interconnector with Victoria went down. Some will not be reconnected until Wednesday. A SAPN spokesperson, Paul Roberts, said in one sense the weekend’s outages were worse than the 2016 event because it would take “a lot longer” to fix as the network had to be rebuilt, not just reconnected. “The statewide blackout was essentially reorganising supply in the network ... building us back up from zero supply,” he told ABC radio on Monday morning. “This is actually about rebuilding the network.” In New South Wales, flash flooding has forced evacuations and seen dozens of flood rescues. Molong, the historic down near Orange, has been completely cut off by flood waters. The State Emergency Service has warned people in Molong’s low-lying area to move to higher ground, as the flash flooding makes it too dangerous to evacuate. An evacuation centre has been set up at the RSL club, and Australian defence force helicopters have been sent in to help rescue trapped people and carry out medical retrievals. Agencies warned at the weekend that storms cells tracking across eastern Australia were likely to bring further stress to many already inundated regional areas in NSW and Victoria. Sign up for Guardian Australia’s free morning and afternoon email newsletters for your daily news roundup A weather system would bring renewed thunderstorms, heavy showers and likely river rises to inland NSW on Monday, which was a concern to the NSW SES, assistant commissioner, Nicole Hogan, said. “We understand this is the last thing you want to hear, with flooding affecting multiple communities in inland NSW,” she said. The Lachlan River was rising at Forbes in the state’s central west on Sunday after experiencing a historic flood a week ago, while a major peak was also occurring downstream at Condobolin, she said. The SES was continuing to support the Forbes community as it recovered from the inundation, she said. The commissioner, Carlene York, urged people to follow warnings and evacuation orders. “Some people are still not listening but they make, regretfully, their decisions based on what they’ve seen in the past,” York said. “But we’ve seen time and time again the water is rising further than perhaps what it has for many years and that’s because of the saturation of the land.” A cold front across NSW on Sunday continued into Monday, bringing storms and adverse weather. Snow is expected in the Alps and central tablelands. The SES has delivered supplies of food, medicine and animal feed to 1,000 residents cut off by flood waters since severe weather began in mid-September, and carried out 500 flood rescues. The volunteer workforce was fatigued and personnel had been requested from other states, York said. Flooding continues across western and southern NSW, in towns including Collarenebri, Walgett, Bourke, Condobolin, Hay and Albury. To the east, some 61mm of rain fell on the northern rivers town of Grafton in just one hour on Saturday night, leading to flash flooding and five requests for SES help. Severe storms with a possible flash flooding risk were forecast across eastern Victoria on Sunday, with intense showers forecast at Seymour, Wodonga, Wangaratta, Corryong, Bright, Mansfield, Falls Creek, Mount Hotham and Mount Buller. Major flooding is continuing at Echuca, Moama, Torrumbarry and Barham along the Murray River. While the Bureau of Meteorology expects heavy rainfall to ease across much of Victoria on Monday morning, the Murray River is not expected to recede later this week.