Victoria’s fight against Covid-19 has intensified after an emergency department nurse tested positive to the virus and health workers descended on two Melbourne suburbs to control community transmission. The state reported 41 new cases on Saturday, amid fears the state was experiencing a potential second wave of coronavirus. Details of the Royal Melbourne Hospital nurse’s case were yet to be revealed on Sunday morning, including what her level of exposure was to fellow staff, patients or visitors. A statement from the hospital said all known contacts had been informed and were receiving support, and the hospital was carrying out additional cleaning and contact tracing. On Saturday, Victoria’s deputy chief health officer, Dr Annaliese van Diemen, said the state had tested almost 22,000 people across several outbreak clusters in the previous 24 hours. Emergency alerts were being sent out to residents in the hotspot Melbourne suburbs of Keilor Downs and Broadmeadows, encouraging them to get tested. Australian defence force medical and support personnel were understood to have arrived in Victoria to help the state’s efforts. About 19,000 people had been through the state’s hotel quarantine system for all overseas arrivals but a significant but undisclosed number had refused tests as they entered isolation. On Friday, Van Diemen said about 70% of people in hotel quarantine had taken the test when offered. On Saturday, she said that number was probably higher, but did not give an exact figure. Victoria’s 41 new cases was the state’s 11th day of double-digit case numbers. There are nearly 1,990 total cases and 204 are active, including five in hospital. The death toll remains at 20. New South Wales authorities on Saturday announced that anyone who refused a test on their 10th day of quarantine would be forced to extend their quarantine for a further 10 days. The state reported six new cases on Saturday. Five of them were returned travellers in hotel quarantine while the sixth was a man in his 70s from Sydney’s west. Less than 2% of returned travellers in hotel quarantine in the state have refused to take a coronavirus test on the 10th day of their stay, NSW Health said. Van Diemen confirmed Victoria was seeking legal advice on whether it could force overseas arrivals entering quarantine to take a test. But she said: “We are not seeing cases in the community that have leaked out of hotel quarantine.” The Liberal MP Trent Zimmerman said returned travellers who did not get tested were “reckless” and said he would support mandatory testing. “If they are not prepared to do that, they shouldn’t come back,” he told ABC television. The Labor frontbencher Linda Burney said returned travellers who refused a test were “really selfish” but she did not go as far as Zimmerman in calling for mandatory testing. Eight of Victoria’s new cases were linked to known outbreaks, 13 had come from community testing and 19 were under investigation. One new case was linked to hotel quarantine, and one more had been added from a reclassification. Victoria’s 41 new cases came after 30 cases reported the previous day, but Van Diemen was reluctant to label the outbreaks as a second wave. She said: “Our case numbers are increasing so when you look at our overall epidemiological curve there will be, and I’m hoping very soon, a second bump or a second peak … Whether we have second, third, fifth, 10th waves, nobody really knows. This is not something any of us have experienced before.” The state has ramped up testing with its focus on 10 suburbs with high community transmission – Keilor Downs, Broadmeadows, Maidstone, Albanvale, Sunshine West, Hallam, Brunswick West, Fawkner, Reservoir and Pakenham. The Queensland government, which is considering easing restrictions faster, recorded no new cases on Saturday and has announced only one new case in more than a week. There were two active cases in the state. The state’s premier, Annastacia Palaszczuk, said an announcement on the opening of the state’s border would be made on Tuesday, but Victoria’s spike was her “No 1 area of concern”. She said: “We don’t want a second wave and we don’t want that community transmission here.” South Australia reported no new cases of Covid-19 over the past 24 hours, with no active cases. However, more than 250 repatriated Australians returned home on a flight from Mumbai via Singapore and will begin two weeks of quarantine in an Adelaide hotel. The state’s health minister, Stephen Wade, warned a number of Covid-19 cases should be expected among the returning passengers but all those arriving would be tested when they landed and while in isolation. Western Australia reported zero new cases on Saturday, with four cases remaining active in hotel quarantine. The state is now in phase four of eased restrictions, with big queues forming outside nightclubs when they reopened at midnight. The gaming floor at Crown Perth reopened at 6am, with spacing requirements in place, and the venue now has about 4,200 staff back at work. Lifting the interstate border closure under phase six has been put on hold due to the spike in cases in Victoria. There are now more than 7,640 confirmed virus cases across the country since the outbreak began, which has seen 104 people die, two of them in the past week. On Saturday, the treasurer, Josh Frydenberg, said he had been assured by the nation’s major banks during talks with himself and the prime minister, Scott Morrison, that they would continue to assist their customers through the pandemic and beyond September when the six-month deferral of mortgage repayments ends. “We recognise some areas of the economy and those workers in it are going to need support for months to come given some of these health-related restrictions remain place,” he said.