GENEVA (AFP) - The Swiss will vote on Sunday (Nov 28) on the country's Covid-19 laws, after a campaign characterised by unprecedented levels of hostility in the wealthy Alpine nation, including even death threats.

Like in much of Europe, Switzerland has seen growing anger over restrictions and vaccine pressure aimed at reining in the pandemic.

But in a country renowned for its culture of compromise, and where referendums take place every few months in a climate of civility and measured debate, the soaring tensions around the upcoming vote have come as a shock.

Police have upped security around a number of politicians, Health Minister Alain Berset included, who have faced a flood of insults and death threats.

"We have seen an increase in threats since the start of the pandemic, with unprecedented virulence," the federal police told AFP.

Fences have also been erected around the government and Parliament buildings in Bern to protect them during anti-vax demonstrations.

Such protests, with their chants of "Freedom! Freedom!", have taken place with increasing frequency across the country.

They are often led by the so-called "Freiheitstrychler", or "Freedom ringers" - men dressed in white shirts embroidered with edelweiss flowers and with two large cowbells suspended from a yoke resting on their shoulders.

The crowds that follow them are fairly diverse, sociologists say, although young men further to the right of the political spectrum are over-represented.

Some of the demonstrations have led to violent clashes with police, who have used rubber bullets and tear gas to rein in the crowds.

"The scale of this is unheard of," Dr Pascal Sciarini, a Geneva-based political scientist, told AFP.

He pointed out that in Switzerland, famous for its direct democracy system, "there are institutional means of expression that tend to temper more heavy-handed and violent forms of protest".

"But when we see what is happening in the streets, it is clear that behaviours are changing," he said.

"Switzerland has become a country like any other," he said. "It is no longer consensus territory, as we still like to believe."

In this climate, observers have warned that Sunday's vote could exacerbate tensions, and even spark a violent backlash among the anti-vax crowd if results do not go in their favour.

It will mark the second time in less than six months that the Swiss have been called upon to vote on the government's response to the pandemic.

In June, 60 per cent of voters approved prolonging national measures.

But opponents insisted a new vote was needed on amendments to the Covid law which, among other things, provide the legal basis for the so-called Covid certificate, indicating that a person has been vaccinated or has recovered from the disease.

Some opponents have said the certificate, which has been required since September for access to restaurants and other indoor spaces and activities, is creating an "apartheid" system.

"This law is discriminatory. It will create a two-speed society," said Ms Agnes Aedo, spokeswoman for the "Friends of the Constitution" group that launched the referendum.

The latest polls show that a clear majority of eligible Swiss voters - around two-thirds - still support the law.

All political parties, except for the populist right-wing SVP, the Swiss People's Party, also back the law.

The SVP is the largest party in Switzerland, and some of its representatives, including Finance Minister Ueli Maurer, have been pictured in "Freiheitstrychler" garb.

Dr Sciarini accused the party of trying to score political points on the back of the growing tensions.

"The SVP is fanning the flames," he said.