Switzerland clocked more than 400 Covid-19 cases in 24 hours on Friday for the first time since April 14, but said it was now overwhelmingly under-40s getting infected.

The Alpine country of 8.5 million people recorded 405 new cases, taking the total to 43,532 since the start of the new coronavirus pandemic.

Stefan Kuster, who heads the Swiss health ministry's communicable diseases unit, insisted the situation was stable, with hospitalisation and death rates low.

He said the reproduction rate -- the number of people infected by each person with the disease -- was lower than one.

Through the whole pandemic period, 39 percent of those infected in Switzerland since its first positive case in February have been aged under 40, statistics show.

But people under 40 are nowadays accounting for three-quarters of new cases, Kuster said according to Switzerland's ATS national news agency.

Despite bordering northern Italy -- the early epicentre of the virus in Europe -- Switzerland was not hit as hard by Covid-19 and did not impose as strict a lockdown as some other European states.

Daily case numbers regularly topped the 1,000 mark in March, but hit a very low and stable level in mid-June. They have been steadily on the rise since then.

The first of three phases easing the restrictions took place on April 27.

Bars and restaurants are open again, as are nightclubs in most cities, although some have since become the scenes of mass infections.

Meanwhile as youngsters return to school, two primary-aged classes near Geneva were shut down on Wednesday, with 39 children placed in quarantine after a replacement teacher tested positive for Covid-19.

Switzerland has now conducted more than a million PCR nasal tests for the virus, with 4.8 percent of the 1,070,910 tests proving positive.

From Monday, people arriving in Switzerland from Croatia, Lebanon, Ukraine and the United Arab Emirates will have to go into mandatory 10-day quarantine, according to an updated country list.

The list already includes Brazil, India, South Africa, the United States and Spain excluding the Canary Islands.

Belgium and Mexico are being removed from the list as of Monday.