An explosion has smashed windows at a coronavirus testing centre in a small town north of Amsterdam, police said.
No-one was hurt in the incident near the testing centre in Bovenkarspel just before 7am local time (6am GMT).
Police in the province of North Holland, 40 miles north of the capital, tweeted that “an explosive went off”, and quickly cordoned off the area.
A probe into the cause of the blast is under way.
Police spokesman Menno Hartenberg said it was unclear whether the testing centre had been deliberately targeted, or when the facility would be able to reopen.
He said it was clear that the explosive did not “get there by accident. But we have no idea at the moment who exactly left it there and what the intention was”.
Police said a metal cylinder that had exploded was found outside the building.
The northern regions of North Holland province have been identified as a virus hotspot in recent weeks, with infection numbers higher than the national average.
In January, rioters torched a coronavirus test facility in the fishing village of Urk on the first night of a 9pm-4.30am nationwide curfew imposed as part of the government’s latest coronavirus lockdown.
Some Dutch lockdown restrictions were relaxed on Wednesday with hairdressers, masseurs and other “contact professions” allowed to reopen if they adhered to strict social distancing and hygiene measures.
Non-essential shops also were allowed to reopen in the Netherlands for the first time since mid-December, though only to very limited numbers of customers who made an appointment in advance.
Health minister Hugo de Jonge tweeted: “For more than a year, we’ve been leaning heavily on the people on the frontline. And then this. Crazy.”
The head of the country’s umbrella organisation for local health services that carry out coronavirus testing called the blast a “cowardly act”.
“Our people have to be able to do this crucial work safely,” Andre Rouvoet tweeted.