The Netherlands braced on Tuesday for a fourth consecutive night of coronavirus anti-lockdown riots, with some shops boarding their windows and sending staff home early for safety.

Dutch police detained more than 180 people on Monday night, where roaming groups set fires, threw rocks and looted stores in several cities.

The Netherlands’ first curfew since World War Two was imposed on Saturday despite weeks of falling infections, after the National Institute for Health (RIVM) said a faster-spreading variant first found in England was causing a third of cases.

A hospital in Rotterdam warned visitors of patients to stay away, after rioters tried to attack hospitals in various cities in the past days.

-We have had riots in the past, but it’s rare to have this for several nights across the entire country- said National Police spokeswoman Suzanne van de Graaf. -It’s not only in known problem areas, but much more widespread.-

Riot police with shields and batons were called out in more than 10 cities, many of which had issued emergency decrees to provide officers with greater powers to conduct searches.

Police had scuffled with rioters in several cities late into the night, chasing them down narrow streets with vans or on foot as helicopters hovered overhead.

In Amsterdam on Monday, groups of youths threw fireworks, broke store windows and attacked a police truck, but were broken up by a massive police presence.

Ten police officers were injured in Rotterdam, where 60 rioters were detained overnight after widespread looting and destruction in the city centre, a police spokeswoman said. Supermarkets in the port city were emptied, while rubbish bins and vehicles were set ablaze.

Two photographers were hurt after being targeted by rock-throwing gangs, one in Amsterdam and another in the nearby town of Haarlem, police said.

Coronavirus infections have been falling in recent weeks, with the number of new cases down by 8% over the past week. A little under 4,000 new infections were reported on Tuesday, the smallest daily increase since Nov 24.

But the RIVM said the situation in the Netherlands was still very serious as a result of the more contagious variant that has caused a massive surge in cases in Britain.

Van de Graaf said much of the aggression during the three days of unrest had been targeted at police officers. More than 470 people have been arrested, with riot police deploying water cannon and officers on horseback in several places.

Schools and non-essential shops across the Netherlands have been shut since mid-December. Bars and restaurants were closed two months earlier. The country’s death toll stands at 13,664, with 956,867 infections to date.