Victoria and the ACT have declared states of emergency as Australia goes into lockdown to combat the spread of COVID-19.

As of Monday at 4pm, 344 Australians tested positive to the coronavirus, five people have died and 23 are recovering in isolation.

In NSW, there has been a “dramatic increase” in infections, with the state’s Health Minister Brad Hazzard confirming 37 new cases overnight, with 1282 cases under investigation.

In an unprecedented move in Victoria, Premier Daniel Andrews declared a state of emergency for four weeks, effective from 12pm on Monday, which would remain in place “for as long as it needs to be”.

The special powers have been declared to enforce the 14-day isolation requirements for all travellers coming into Australia, he said.

“Make no mistake, the next few weeks and months will be tough for everyone, but we’re doing what is necessary to protect Victorians,” Mr Andrews told reporters on Monday morning at 8.30am.

This means authorised officers can detain people, restrict movement and prevent entry to premises to protect the public.

Anyone who does not voluntarily comply with the new order could face fines of up to $20,000.

Non-essential mass gatherings of more than 500 people such as cultural and sporting events and conferences, are banned.

Businesses large and small are also being advised to look at the option of employees working from home for the next two weeks.

• Read the full statement here, and penalties for non-compliance

In the ACT, Chief Minister Andrew Barr declared a public health emergency in Canberra minutes after Victoria’s decision, and coming after the nation’s capital confirmed a man in his 30s tested positive over the weekend.

Mr Barr said the declaration would give Canberra’s chief health officer more powers to enforce isolation and quarantines.

In Tasmania, everyone arriving in the state from Tuesday [March 17] would have to provide contact details as part of measures to combat the spread of coronavirus.

They will also need to fill in an ‘arrival card’ that will be rolled out at ports and airports, Premier Peter Gutwein said, adding that filling out the card will be mandatory and will allow the state government to pass on health advice if needed.

And in Western Australia, hefty fines of up to $50,000 come with anyone defying the state of emergency declaration.

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Mr Andrews said Victoria was taking its drastic action “after agreement from the National Cabinet that includes the Prime Minister and all premiers and chief ministers, to contain the spread of coronavirus as much as we can”.

“It is an offence under the Public Health and Wellbeing Act to not comply with the orders that have been made,” he said.

NSW confirms more cases overnight

In NSW, emergency powers have also been introduced to force the immediate cancellation of public events of more than 500 people, with fines of up to $11,000 for those who break the laws.

And Transport for NSW is urging commuters to avoid travelling on public transport during the peak-hour rush if possible to help slow the spread of the coronavirus.

“While staff have boosted maintenance and cleaning efforts on the network in response to COVID-19, customers need to take extra precautions too,” Transport Minister Andrew Constance said in a statement on Monday.

It comes as state health authorities confirmed an additional 37 people tested positive to the coronavirus, bringing the state total to 171.

Mr Hazzard told reporters on Monday afternoon severe penalties would also be imposed if people breach the new quarantine order.

“I stress that it is quite a serious scenario, because people will be liable for individual fines of up to $11,000 if they breach that direction and they may be also liable … for up to six months’ imprisonment.

“Obviously the New South Wales government – indeed all governments around the country – are not wanting to impose penalties on people.

“What we’re looking for is co-operation,” he said.

Self-isolation sanctions introduced on Sunday

The self-isolation sanction was declared by Prime Minister Scott Morrison on Sunday.

Institutions such as the National Gallery of Victoria, State Library, and museums are temporarily closed, while the Melbourne Comedy Festival and Food and Wine Festival have already been postponed.

“This is about flattening the curve,” Mr Andrews said.

While a handful of schools have closed, no announcement has been made to stop students attending schools, TAFEs, universities and early childhood centres. However, camps, extra-curricular activities including music, drama and band practice, and excursions have ceased in many schools until further notice.

• Related: Coronavirus death toll in Australia rises to five

On Sunday, Victorian authorities recommended the public have a two-week stockpile of food – but no more – in preparation for a major coronavirus outbreak in the state.

Mr Andrews said it would be “sensible” to have extra staples on hand as the number of cases of COVID-19 rose.

But he warned against panic buying as it would impact those “most at risk of being quite seriously ill”.

“It is sensible to try to have some of those (staples) on hand, more than you would normally have,” Mr Andrews said on Sunday.

“But if everybody goes out and buys not two weeks worth of staples but two months worth, the shelves will be empty and the only people who suffer then are vulnerable people who might not have got to the shops, or can’t go to four different supermarkets and get the basics that they need.”

Supermarkets Coles and Woolworths, meanwhile, have imposed purchasing limits on staples such as rice, flour, pasta, toilet paper, tissues and hand sanitiser to two units per customer.