SYDNEY, Aug 10 (Reuters) - Australia's Victoria state reported a slight rise in new COVID-19 cases on Tuesday, raising the prospect of an extended lockdown in Melbourne as officials battle to contain a Delta strain outbreak.

State officials reported 20 new cases, up from 11 a day earlier, and added dozens of new venues to a list of virus-exposed sites in Melbourne, including cafes, supermarkets and fuel service stations.

In line with recent trends, and worrying officials, 15 of the cases were in the community while infectious. Health officials have said the number of people who are in public while infectious needs to be close to zero before lockdowns in Sydney and Melbourne are lifted. read more

Melbourne's lockdown is currently scheduled to end on Thursday and Sydney's at the end of the month.

New South Wales officials expanded strict stay-home rules to include two regions near the Queensland border, Byron Bay and Tamworth, late on Monday after visits by infectious people from the city.

With just over 36,600 cases and 939 deaths, Australia has handled the pandemic much better than many other developed economies.

But the fast-moving Delta strain has thrown Australia's reopening plans in disarray. Economists expect the lockdowns in its two largest cities to have tipped the country's A$2 trillion ($1.5 trillion) economy into a second recession in as many years.

"There are big challenges for the economy, but I want people ... to be confident, to be optimistic and to know there is going to be light at the end of the tunnel," Federal Treasurer Josh Frydenberg told broadcaster Seven News on Tuesday.