Denmark will make the wearing of face masks mandatory on public transport across the country from August 22 to try to contain the coronavirus, Prime Minister Mette Frederiksen said Saturday.

She called on Danes not to let down their guard and to respect social distancing and hygiene rules.

Danish authorities currently recommend masks on public transport during peak times, while they are obligatory in six areas including the country's second city of Aarhus, where the outbreak of the virus is greater.

"We have witnessed a rise in the number of people infected in Denmark, with several local clusters," said Tyra Grove Krause, an official from the country's infectious diseases control authority.

"Some (outbreaks) are under control and others are about to be."

Denmark has registered a total of 15,859 cases of COVID-19 with 621 deaths.