A bomb attack on a Dutch coronavirus test centre shortly before it was to open was labelled "insane" by the country's health minister.
The pipe bomb exploded at 6.55am on Wednesday in the town of Bovenkarspel, 55 kilometres north of Amsterdam, shattering windows but causing no injuries to passers-by or the security guard on duty.
The attack comes weeks after a testing centre was burned down during riots across the Netherlands against a coronavirus curfew.
Officers said the explosion appeared to be deliberate.
"It's not possible that this was by accident, the object was placed there and exploded near the front of the test centre," police spokesman Menno Hartenberg said.
"We are not ruling anything out and can't say anything about a motive. An investigation is under way.
"The bomb was a metal object somewhere between a tube and a canister."
The GGD, the Dutch health service which runs the national testing scheme, described the attack as “aggressive and intimidating vandalism”.
"Our people must be able to do this crucial work safely. This cowardly act of destruction affects us all," GGD president Andre Rouvoet said on Twitter.
Health Minister Hugo de Jonge said public health authorities were "terribly shocked".
"For over a year now, we have relied heavily on the people on the front lines. And then this. Insane," he said.
A bomb squad was sent to determine whether any explosive material remained at the scene.
The explosion comes two weeks before national elections on March 17, widely seen as a referendum on the government's handling of the pandemic.
The region around Bovenkarspel is in the grips of one of the country's worst Covid-19 outbreaks, with 181 cases per 100,000 people, compared with about 27 per 100,000 nationally.
At least one hospital was forced to send patients to other provinces due to lack of space in its intensive care units.
Anger against national Covid-19 restrictions increased dramatically at the start of the year.
In January, a Covid testing centre was set on fire in the Dutch village of Urk as protests broke out after the government introduced a 9pm-4.30am curfew, and limited the number of guests people could have in their homes to one a day.
The Netherlands suffered several nights of rioting, the country's most violent in decades.
Two weeks ago, a court found that the curfew was illegal because it violated freedom of movement and assembly. The decision was overturned on appeal.
After weeks of lockdown, certain measures were eased on Wednesday, with hairdressers reopening and non-essential shops allowed to accept a small number of visitors by appointment.
