Infectious disease experts cautioned that the results could not be interpreted as evidence that lockdowns were unnecessary but acknowledged they may indicate Sweden's overall stance on fighting the pandemic had merits worth studying.

In the past week, Germany and France have extended lockdowns amid rising coronavirus cases and high death tolls, moves that economists say will further delay economic recovery.

While many Europeans have accepted lockdowns as a last resort given the failure to get the pandemic under control with other methods, the moves have in recent months prompted street protests in London, Amsterdam and elsewhere.

Sweden, meanwhile, has mostly relied on voluntary measures focused on social distancing, good hygiene and targeted rules that have kept schools, restaurants and shops largely open - an approach that has sharply polarised Swedes but spared the economy from much of the hit suffered elsewhere in Europe.

Preliminary data from EU statistics agency Eurostat compiled by Reuters showed Sweden had 7.7 per cent more deaths in 2020 than its average for the preceding four years.

Countries that opted for several periods of strict lockdowns, such as Spain and Belgium, had so-called excess mortality of 18.1 per cent and 16.2 per cent respectively.

Twenty-one of the 30 countries with available statistics had higher excess mortality than Sweden.

However, Sweden did much worse than its Nordic neighbours, with Denmark registering just 1.5 per cent excess mortality and Finland 1.0 per cent.

Norway had no excess mortality at all in 2020.

Sweden's excess mortality also came out at the low end of the spectrum in a separate tally of Eurostat and other data released by the UK's Office for National Statistics last week.

That analysis, which included an adjustment to account for differences in both the age structures and seasonal mortality patterns of countries analysed, placed Sweden 18th in a ranking of 26.

Poland, Spain and Belgium were at the top.

Sweden's Chief Epidemiologist Anders Tegnell, a largely unknown figure before the pandemic who became internationally known as the figurehead of the Swedish response, told Reuters he believed the data raised doubts about the use of lockdowns.

"I think people will probably think very carefully about these total shutdowns, how good they really were," he said.

"They may have had an effect in the short term but when you look at it throughout the pandemic, you become more and more doubtful," said Tegnell, who has received both death threats and flowers as a token of appreciation.

Other health experts warn that interpreting excess deaths data is fraught with risks of ignoring crucial variables.

"All of us have to be really careful interpreting death data connected with COVID-19, whatever its source - none of them are perfect," Mark Woolhouse, professor of infectious disease epidemiology at the University of Edinburgh in the UK, told Reuters.

"They do raise a question about whether, in fact, Sweden's strategy was relatively successful. They certainly raise that question," he said, commenting on data first published in Swedish media and checked by Sweden's statistics office.

Keith Neal, University of Nottingham professor in infectious diseases, also advised caution.

He cited a range of factors such as the age structure and general health of a population, average household size and whether a country had megacity travel hubs as significant.

Sweden's government and health authority have conceded they failed to protect Sweden's elderly but maintained they did what they could to suppress the disease, while also taking general health of the population into account.

Sweden's official COVID-19 death toll is more than 13,000, although some people may have died from other causes than the disease.

Australian Associated Press