SYDNEY - In Australia, where borders between states are often marked by little more than a sign on a dusty road, many travellers may not even know when they have crossed from one state to another.
But the Covid-19 pandemic - and the uneven geographic spread of the virus - has suddenly changed this and prompted states to put up borders and fence themselves in.
Several, including South Australia, Western Australia and Queensland, started shutting their borders last week - a move that would have been unthinkable before the outbreak.
Travellers who cross the border will be forced to self-isolate for 14 days.
The island state of Tasmania and the Northern Territory have introduced similar closures.
Announcing the Queensland closure, the state's Premier, Ms Annastacia Palaszczuk, said the border would remain open only for freight and essential travel. Those who breach the quarantine could face fines of up to A$13,345 (S$11,740).
"We don't want people from New South Wales and Victoria coming up here to Queensland," she said. "People should stay in their own state, and where possible they should be staying in their suburbs, and as much as possible staying at home."
As of Sunday morning (March 29), Australia had 3,809 confirmed cases of the virus with 16 deaths.
Last week, the confirmed cases were clustered disproportionately across the country.
The most populous state, New South Wales, for instance, has 32 per cent of the population but 1,219 cases, amounting to 44 per cent of the national total.
In contrast, Victoria, which has 26 per cent of the population, has 520 cases, or 19 per cent of the total.
Australia has not experienced these sorts of border closures since the Spanish flu pandemic in 1919. But the moves have already hit some obstacles.
Many people who live in northern New South Wales, for instance, work in Queensland, but will now need special permits to enter.
During the first day of the closure, passage was relatively smooth and motorists cooperated, though some areas had heavy traffic.
Some international holidaymakers on long-distance road trips have been caught in remote areas and will no longer be able to complete their journeys. An estimated 75,000 holidaymakers are currently in caravan parks around the country.
There have also been questions about whether the closures are permitted by the federal Constitution, which provides for free movement of people and goods between states.
However, a constitutional law expert, Professor Anne Twomey from the University of Sydney, said states were entitled to take necessary measures to protect health, even if this obstructed trade. She said the states were not barring people from crossing borders but instead imposing health checks and requirements to self-isolate.
"No one could argue that the reason is 'protectionist' or simply an objection to residents from other states entering the state," she wrote on The Conversation website.
In Australia, states control basic services such as hospitals, schools, public, transport and police. But the nation is heavily centralised and the bulk of power lies with the Federal government, which oversees trade, defence, immigration and universities.
Unlike in the United States, different Australian states do not have distinctive accents or identities, and there is far less commitment to defending state rights.
Indeed, there has long been debate in Australia about whether to abolish the states. But the outbreak appears to be strengthening their roles.
In an unusual move, Prime Minister Scott Morrison joined with the country's eight state and territory leaders to form a wartime-style national Cabinet that is coordinating the response to the outbreak. The Cabinet meets several times a week by video conference.
A political commentator, Mr Tom Burton, said the Cabinet was an "extraordinary" creation that has defied those who believe Australia's federal structure is an impediment to good economic and social policymaking.
"Australia's first national Cabinet is finally doing what countless reviews… have pleaded for," he wrote in The Australian Financial Review. "Governments of all colours, and their agencies, working as one, in a form of cooperative federalism many officials had only dreamed of."