The World Health Organization (WHO) has urged countries not to lift measures put in place to slow the spread of the coronavirus too early.

"One of the most important parts is not to let go of the measures too early in order not to have a fall back again," said WHO spokesman Christian Lindmeier in a virtual briefing on Tuesday.

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"It's similar to being sick yourself if you get out of bed too early and get running too early you risk falling back and having complications," he added.

Neil Ferguson, an epidemiologist with Imperial College London and adviser to UK Prime Minister Boris Johnson, said rules could be relaxed if the country moved more towards mass testing.

"We want to move to a situation by at least the end of May where we can substitute some less intensive measures - more based on technology and testing - than the current lockdown," Ferguson told the BBC.

Denmark said it would move towards a "careful" reopening of parts of the country in the coming weeks.

The country's Prime Minister Mette Frederiksen said on Monday that after Easter, her government would open primary schools, daycare centres and kindergartens for the first time in almost a month.

However, she stressed that if there were a sudden increase in coronavirus cases after Easter, the plans would be immediately suspended.

In Austria, the government laid out a timetable for letting shops shuttered because of the pandemic to reopen in phases starting a week from Tuesday.

"We reacted faster and more restrictively than in other countries and could, therefore, avoid the worst. But this fast and restrictive reaction now also gives us the possibility to come out of this crisis more quickly," Chancellor Sebastian Kurz said in a news conference.

But Kurz cautioned that authorities could activate an "emergency brake" if the cases rise again.

Speaking in Vienna, Kurz said the government's plan is to reopen small shops of less than 400sq metres (4,305sq feet), hardware stores and garden centres on April 14.

Europe has been hit hard by the coronavirus pandemic, with countries like Spain and Italy reporting more than 270,000 confirmed cases combined, and over 30,000 fatalities, according to data compiled by Johns Hopkins University.