MELBOURNE, Dec 4 (Reuters) - The Omicron coronavirus variant spread in Australia on Saturday, testing plans to reopen the economy as a cluster in Sydney grew to 13 cases and an infection was suspected in the state of Queensland. Federal authorities are sticking with a plan to reopen the economy on the hope that the new variant proves to be milder than previous strains, but some state and territory governments have moved to tighten their domestic border controls. Australia reported its first community transmission of Omicron on Friday at a school in Sydney. Authorities are investigating the source. Further Omicron cases were expected over the weekend when more tests results come, said Kerry Chant, chief health officer of New South Wales, of which Sydney is the capital. Queensland authorities said the state suspected its first Omicron case in a person who travelled from South Africa and that genome sequencing was ongoing. "The public health unit have ruled out that it is Delta but we haven"t been able to confirm if it is Omicron," state Health Minister Yvette D"Ath. "But it is being treated as if it is." The Australian Capital Territory, home to the capital Canberra, was on alert for further spread after one of its new coronavirus cases was found to be a close contact of the Territory"s first Omicron case reported on Friday. Authorities in South Australia said on Saturday that arrivals from New South Wales, Victoria and the capital territory will be tested. The state reopened its domestic borders only days ago for the first time in months. Despite battling many outbreaks this year, leading to months of lockdown in Sydney and Melbourne - Australia"s largest cities - the country has had only about 834 confirmed COVID-19 cases and 7.9 deaths per 100,000 people, according to the World Health Organisation, a fraction of impact in many other developed nations. Australia has had just under 215,000 cases total and 2,042 deaths.