"It's clear that in Iran there is an uncontrolled spread," Health Minister Greg Hunt said. "The situation in Iran is clearly far worse than has been documented and significantly higher than the recorded case numbers."

Australians are being told not to travel to Iran and if they are there to get out while they can. Embassy families have been ordered home.

"Airlines are reducing or stopping flights into and out of Iran. Medical evacuation is not likely to be possible," the government's travel advice warns. "If you're in Iran, leave while commercial options are available."

The coronavirus cases in Australia were limited until last week to people connected with an early Wuhan tour group, 15 of whom were infected, and to Diamond Princess cruise ship passengers, 10 of whom were infected.

But numbers stood on Wednesday at 41, with most of the new cases among travellers returned on separate flights from Iran. One was in a man who had travelled to Singapore and another case in a Chinese student who had spent two weeks in Dubai. Two of the NSW cases - doctor and an aged care worker having not travelled and with no known source - indicate the virus is already circulating in the community.

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On Wednesday new virus cases were confirmed in South Australia, Victoria and Queensland, all among people who have travelled from Iran. On Tuesday, Tasmania reported its first case, also in a traveller from Iran. Health authorities in Tasmania say the man went to a supermarket on his way home despite being told to stay in isolation, according to media reports.

Around the country, there is now a scramble to track down passengers who have shared domestic and international fights with the new cases.

On March 1, Australia imposed a travel ban on Iran, which bans anyone who is not an Australian citizen, permanent resident or close family member from entering Australia. Residents and citizens who return are asked to self-isolate for 14 days. The compulsory self-isolation has now been backdated to February 19.

Mr Hunt said about 900 people travelled from Iran to Australia each month.

With the coronavirus expected to slam global economic growth and badly impact Australia's economy and budget, Prime Minister Scott Morrison has upped his rhetoric

He described the virus as "a very dramatic situation" with very serious health effects and "very real and significant economic impacts".

"What this health crisis is doing is disrupting supply chains and disconnecting travellers from where they would otherwise have gone, it is disconnecting exporters from their markets. It is disconnecting and disrupting the global economy."

Earlier, Chief Medical Officer Brendan Murphy said authorities were considering making a recommendation about the upcoming Iranian New Year celebrations.

He told Senate estimates hearings that Iran was a greater risk than China. The China travel ban had been a success, with only one case sourced to mainland China during the ban. More than 30,000 Australian citizens had returned with no positive rests among them.

Asked about the 99 non-Australians who had been given exemptions to the travel ban, allowing them to enter Australia, Professor Murphy said the exemptions were at the discretion of the Border Force Commissioner and he was not consulted on individual cases, but the national health committee was happy with the "very careful small approval".

Small numbers with an absolute guarantee of safe quarantine, such as the 700 high school students allowed in, were not a material risk to the community, he said. Exemptions should not be granted to tourists because they could not be quarantined in hotels, he said.