There's no shortage of clamouring on social media for the closure of Tasmania's border to protect residents of the island state from COVID-19. So, is it time to raise the drawbridge?

"I am postponing my holiday to Tassie out of respect for my loved ones there! Close it down!" one woman posted on social media.

"They should close all borders until this crisis is over," another one wrote.

Some have urged caution because of the complexities involved.

"The hidden consequences for Tasmania are significant if the borders close," a woman wrote in a post.

So, could Tasmania close its borders? And if so, what would it achieve?

Is it legal?

An unsupported and unilateral bid by the Tasmanian Government to close its borders could end in the High Court.

George Williams, the dean of law at the University of New South Wales, said there were a lot of practical challenges in closing a border, but there was also a constitutional one.

"We have section 92 of the Australian constitution and it says trade, commerce and intercourse amongst the states shall be absolutely free," Professor Williams said.

"The idea is that we are one country, and a person should be entitled to travel around Australia as they wish."

Professor Williams said there were sometimes exceptions even for something as clearly expressed as that.

"So if it was felt that the border needed to be closed for a genuine health emergency and this was a proportionate and appropriate response, somebody could argue that they are entitled to close the border," he said.

"If a person wanted to challenge that, it could be referred to the High Court."

Tasmania might have a better chance than other areas in Australia as an island, in the appropriate medical emergency.

"Tasmania is in a unique position, and could contemplate this in a way that would not be so possible in another part of Australia," Professor Williams said.

"But even then there is a lot of commerce and a lot of travel, into Tasmania and out, and it would be both hard to justify and hard to implement, and there would be that possibility for constitutional challenge.

"If there is a genuine and strong reason why Tasmania should do it, backed by the best medical advice, and if it was done in a way that was proportionate and appropriate for the circumstances, then it might survive constitutional challenge."

Could Tasmania stop planes and ships arriving?

Tasmania has already stopped cruise ships from docking, but plenty of other ships arrive around the state. ( ABC News: Fiona Blackwood )

Professor Williams said Tasmania could attempt to stop flights or ships coming into the state — cruise ships have already been banned from docking in the state until June 30.

"But it gets a bit more tricky at that point, because a lot of these are managed at the national level by the Commonwealth, and there is a possibility that any Tasmanian law would be inconsistent with federal law," he said.

"Under section 109 of the constitution, if there is a conflict [between a federal and a state law] the federal law takes precedence.

"So once you get into areas that are clearly subject to federal regulation you could only proceed at a state level if you have Commonwealth support and the Commonwealth essentially providing room for the state to charter its own course.

"If you have a Commonwealth law that gives people permission to come into Tasmania, and a Tasmanian law that says the opposite, probably what would happen is the Commonwealth law would remain in effect and the Tasmanian law wouldn't have any work to do."

So if borders closed, would that protect Tasmanians?

Kirsty Short, an influenza virologist from The University of Queensland, said the effectiveness of border closures depended on the level of community transmission that existed, as opposed to person-to-person transmission.

"Person-to-person transmission is just, 'I am infected and I infect you'," Dr Short said.

"Community transmission is when an individual is infected, and they have no known contacts with someone who is infected, they haven't been overseas. So essentially we don't know how they got infected."

She said in case of community transmission closing the borders would not necessarily help.

"It will help in reducing imported cases, but it's not going to help with cases already there," she said.

Dr Short said Tasmania had no community transferences yet.

"What we know from history is that early border closures, provided there was no community transmission, would probably have an effect on reducing the number of cases," she said.

"But again I would say it is a pretty dramatic measure to take because of the knock-on consequences."

She said Australia was sitting in "quite a good place".

"We don't have widespread community transmission. We've implemented [national controls] at a good time," she said.

How does it all add up?

Mathematician James Wood from the University of News South Wales said at the moment Australia had about 250 identified cases in a population of 25 million.

"So [that's] around one-thousandth of 1 per cent," Associate Professor Wood said.

"[Around] 3 million travellers [are] coming through Hobart airport per year — not all of these from out of state — so about 8,000 per day.

"So if all these infected people were equally likely to travel as anyone else — and I don't think they would be — you might have at most about 8 per cent chance per day at the moment of an infected case coming through from interstate, or maybe about 1 person per fortnight.

"That of course could change with time, but that's a pretty manageable number for your public health authorities to identify and follow up."

Professor Wood said when he looked at a pandemic plan in 2006, analysis was that internal border control wasn't particularly useful.

"It could come back on the agenda if we have trouble containing our jurisdictional outbreaks, but at present I would not think it's not a high priority for Tasmania to shut its borders," he said.

In a statement, Premier Peter Gutwein said it was an evolving situation.

"We will continue to make the best decisions for the health and wellbeing of Tasmanians, taking advice from our public health experts," he said.

"We have not made the call to close our borders nor have we received advice to do so, however we will continue to be informed by our public health experts on this matter."