Sweden's government has introduced the toughest measures yet to help stave off a second wave of the pandemic, including recommending masks on public transport and closing non-essential public workplaces.

Sweden has stubbornly resisted lockdowns and has left most schools, businesses and restaurants open throughout the pandemic.

However, a severe second wave of the pandemic, with record numbers of new cases almost every week for the past two months, has prompted the government to do more.

Prime Minister Stefan Lofven said non-essential public workplaces, such as gyms, pools and libraries, would close until 24 January.

 He also said the government now recommended using masks on public transport during crowded hours.

"We are doing what we have done throughout this pandemic, the right measures at the right time. And this is what this is," Mr Lofven said.

Asked about whether stricter measures were necessary Lofven maintained that the strategy was calibrated for the long-haul.

"A serious lockdown would not have an effect in the long run because people would not put up with that," Mr Lofven told reporters.

But as cases have risen, authorities have urged people to limit social interactions to those in their household or a very small circle of friends.

However, some measures are binding, and on 24 November a ban on public gatherings of over eight people came into force, lowering the number from 50.

With the number of deaths close to 8,000 Sweden's death rate per capita is several times higher than that of its Nordic neighbours but lower than several European countries that opted for lockdowns.

Johan Carlson, director of the Public Health Agency, has stressed that face masks should not be considered a substitute for maintaining physical distance, and the recommendation was limited to situations were that was impossible.

"We don't think it will have a deciding effect, but in this specific situation it can have a positive effect," Mr Carlson said, adding that wearing them in the street did not seem to be significant.

Read the latest coronavirus stories

Sydney residents urged to stay home as cluster grows

Australian officials have declared Sydney's northern beaches a coronavirus hotspot as a cluster of cases grew to 28 and triggered a return of domestic travel restrictions.

The outbreak follows a period of relative normality in the city after it proved a success in keeping a lid on the virus in recent months.

But today hundreds of thousands of residents were urged to stay home as much as possible for three days and long queues formed outside Covid-19 clinics as health officials raced to contain the infection.

Premier Gladys Berejiklian, leader of Sydney's state of New South Wales, said: "If we get on top of this in the next two or three days, all of us will be able to have a much better Christmas.

"But if we don't get on top of it in the next few days, it could mean further restrictions down the track."

Despite most cases being linked to a venue in the suburb of Avalon on the city's northeast peninsula, Berejiklian said all of greater Sydney's over five million residents should be on "high alert".

Mask wearing, although encouraged, remains optional in Sydney as daily community cases in Australia have remained low or at zero for months.

Success in containing the virus has allowed a continued rollback of restrictions ahead of Christmas, with domestic travel having returned largely to normal before the latest outbreak.

The loosening of curbs has sparked fears that the new outbreak could have already spread around the country.

One case linked to the cluster has been detected in neighbouring Queensland, prompting state and territory officials to announce restrictions on travellers from Sydney, forcing many into isolation.

Some of the toughest restrictions have come from Western Australia, with the state's leader Mark McGowan announcing a 14-day self-quarantine for all arrivals from New South Wales.

Mr McGowan said: "There is no doubt New South Wales is on the verge of a serious outbreak, and we must do whatever is required to keep us safe."

Health officials said genomic testing had found the strain of the virus was likely from the United States but how it spread to Sydney was unclear.

Overseas arrivals in Australia are strictly controlled and required to quarantine.

A bus driver who transported air crew from the city's airport also tested positive for an overseas strain of the virus earlier this week, but he is not linked to the northern beaches cluster, officials said.

Australia has recorded over 28,000 coronavirus cases and 908 deaths in a population of 25 million.