An estimated 35,000 people gathered in central Brussels on Sunday to protest against the reinforced measures, which include the mandatory use of the 'COVID Safe Ticket' (CST) and the obligation to wear face masks in areas where a CST is required, reports Xinhua news agency.
The demonstration took place near the Brussels North Station, with protesters brandishing banners saying "Together for Freedom" and "Resistance".
The police used water cannons and tear gas to subdue demonstrators who threw fireworks at them.
Forty-two people were detained and two arrested, local police said late on Sunday and the mayor of the City of Brussels, Philippe Close, "strongly condemned" the riots.
In Rotterdam, the demonstration against the Covid-19 restrictions started on November 19 when several hundred protesters gathered in the city centre throwing fireworks and setting cars -- among them at least one police vehicle -- ablaze.
The protest escalated into riot, and the police responded with water cannons and tear gas.
Around 50 people were arrested and four were injured and sent to hospital for treatment.
On Monday, Dutch Prime Minister Mark Rutte condemned the riots and warned that everything possible would be done to punish the rioters.
"These are not corona protests, but pure violence by idiots, which has nothing to do with demonstrating," Rutte said after consulting his fellow ministers.
Across Greece, restaurants and cafes remained closed lin protest against the government's new restrictions.
The measures have hit thousands of businesses, with many of them facing the risk of permanent closure, and further state support is urgently needed, the Panhellenic Federation of Restaurants and Related Professions (POESE) said on Monday.
"We are shutting down today so that we will not have to shut down forever," protesters chanted during a rally held in the center of Athens.
"Catering stays closed throughout Greece" read banners on the closed doors of restaurants and cafes.
With the onset of the winter season in the Northern Hemisphere, the European Union (EU) fears a new wave of Covid-19 infections.
The level of concern for the situation in the EU was rated at 8.3 of 10, or "very high" on November 19 by the European Center for Disease prevention and Control (ECDC).
Wearing masks, hand-washing and ventilation are crucial non-pharmaceutical measures that must continue in order to fight Covid-19, and "it remains extremely important that we follow the non-pharmaceutical interventions", Stefan De Keersmaecker, European Commission spokesperson for Health, said on Monday.
French Minister of Labour Elisabeth Borne on Monday called on companies to strictly respect barrier gestures, especially the mask mandate, in order to enable the country to face the fifth Covid-19 wave.
In light of the worsening situation, France's Vaccine Strategy Orientation Council (COSV) on Monday suggested that a booster shot for all adults should be considered.
In the face of the growing pandemic, Germany's federal states have recently tightened their respective Covid-19 measures.
The states of Bavaria and Saxony have cancelled their Christmas markets this year, and Hesse decided that only those vaccinated or recovered from Covid-19 will be allowed to enter indoor areas of restaurants, sports facilities and cultural institutions.