* Australia has reported more than 5,200 infections and 25 deaths
* Several states are strengthening border controls
By Jonathan Barrett and Renju Jose
SYDNEY, April 3 (Reuters) - The leader of Australia's most populous state, New South Wales, said on Friday that authorities did not plan to impose further lockdown restrictions, despite concerns more coronavirus cases were emerging without a known source.
New South Wales (NSW) remains the epicentre of the disease in Australia, although the rate of infection has fallen steeply in recent days.
"If all of us stick to the rules, don't leave the house unless we absolutely have to, we will be able to some extent control and contain the spread," said NSW Premier Gladys Berejiklian, who added that there were no plans to bolster current measures.
NSW residents are subject to a public order that allows for fines of up to A$11,000 ($6,667) and prison time for those who breach strict social distancing rules. The order is due to run for 90 days.
Berejiklian said in Sydney on Friday that while infection rates were stabilising, health authorities were grappling with an increased number of cases without a known source.
"If we can't identify the source it means we can't deal with the spread - that is something we're worried about."
NSW accounts for just under half of the nation's confirmed cases, which now exceed 5,200. There have been 25 deaths across the country.
State border controls were bolstered on Friday, with water barriers and checkpoints preventing all non-essential travel into Queensland, which shares a border with NSW.
Several states have introduced border controls in recent days for the first time since the Spanish flu epidemic 100 years ago.
Tasmania, an island off the mainland's south-east coast, is all but isolated, while the iron ore-rich state of Western Australia is enforcing a "hard border close" from Monday.
Australia also has to decide what to do with more than a dozen cruise ships it has banned from docking at its ports. The issue has been a source of public angst in the country after hundreds of infections were traced to cruise ship passengers and returning travellers.
NSW Police commissioner Mick Fuller said on Friday that five Royal Caribbean ships off the country's east coast will depart for their port of origin after refuelling and restocking on the weekend.
($1 = 1.6499 Australian dollars)