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Tens of thousands of people have been marching in the Belgian capital, Brussels, to protest against anti-Covid measures.
Some protesters threw fireworks at police officers, who intervened with tear gas and water cannon.
Demonstrators are mainly opposed to the use of Covid passes, which stops the unvaccinated from entering venues such as restaurants or bars.
This comes after fresh protests in the Netherlands against new lockdown rules.
On Saturday, people hurled fireworks at police and set fire to bicycles in The Hague, one night after protests in Rotterdam turned violent and police fired gunshots.
Thousands of demonstrators also took to the streets in Austria, Croatia and Italy as anger mounted over new curbs.
In Belgium, rules on face masks have been tightened, including in places such as restaurants where Covid passes are already required, and most Belgians will also have to work from home four days a week until mid-December. There are also plans to make vaccinations for health workers compulsory.
Earlier, the World Health Organization (WHO) said it was "very worried" about rising coronavirus cases on the continent.
Its regional director, Dr Hans Kluge, told the BBC that unless measures were tightened across Europe, half a million more deaths could be recorded by next spring.
"Covid-19 has become once again the number one cause of mortality in our region," he said, adding "we know what needs to be done" in order to fight the virus – such as getting vaccinated, wearing masks, and using Covid passes.
Many governments across the continent are bringing in new restrictions to try to tackle rising infections. A number of countries have recently reported record-high daily case numbers.
In the Netherlands, a second night of riots broke out on Saturday in several towns and cities.
Hooded rioters set fire to bicycles in The Hague, as riot police used horses, dogs and batons to chase the crowds away. Officials announced an emergency order in the city, and at least seven people were arrested.
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Police said a rock was thrown through the window of an ambulance carrying a patient. Officers in the city tweeted that five police officers were injured, with one taken away by ambulance with a knee injury.
Elsewhere in the country, two top-flight football matches were briefly halted after supporters broke into the grounds and ran on to the pitch. Fans are currently banned from stadiums because of new coronavirus rules.
The unrest followed a night of riots in Rotterdam condemned by the city's mayor as "an orgy of violence". Police fired warning shots and direct shots "because the situation was life-threatening", a police spokesperson told Reuters.
At least three demonstrators are receiving hospital treatment for gunshot wounds, officers said. Authorities have launched an investigation.
The Netherlands imposed a three-week partial lockdown last weekend after recording a record spike in Covid cases. Bars and restaurants must close at 20:00, and crowds are banned at sports events.
Tens of thousands of people protested in Austria's capital, Vienna, after the government announced a new national lockdown and plans to make jabs compulsory in February 2022. It is the first European country to make vaccination a legal requirement.
Brandishing national flags and banners reading "Freedom", protesters shouted "Resistance!" and booed the police.
The country will enter a 20-day nationwide lockdown from Monday, shutting all but essential shops and ordering people to work from home.
The mandatory vaccinations have been described as a "double-edged sword" by Andrea Ammon, director for the European Centre for Disease Prevention and Control.
She told the BBC's Andrew Marr that the strict rules could make people who were still doubting the vaccine – but not fully rejecting it – completely turn away from it.
In Croatia, thousands marched in the capital, Zagreb, to show their anger at mandatory vaccinations for public sector workers, while in Italy, a few thousand protesters gathered at the ancient Circus Maximus chariot-racing ground in Rome to oppose "Green Pass" certificates required at workplaces, venues and on public transport.
French authorities are sending dozens more police officers to quell unrest on the Caribbean island of Guadeloupe, a French overseas department.
Overnight riots saw looters ransack dozens of shops and set businesses alight after protests against France's own Covid pass turned violent.
Interior Minister Gérald Darmanin said that some involved in the unrest used "live ammunition" against law enforcement, and promised a "firm" response to those committing public disorder.
UK Health Secretary Sajid Javid has said there are no plans to change travel rules between the UK and Germany at the moment, in view of the rising number of cases there.
He said this was because Germany was dealing with the Delta variant: "We have Delta here already, I'm not sure there is much benefit in having more rules, but we do keep an eye out for any potential new variants," he told Andrew Marr.
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