A coronavirus test centre near Amsterdam has been deliberately hit by a pipe bomb explosion, according to police.
The blast in the town of Bovenkarspel, north of the Dutch capital, at around 6.55am this morning shattered windows but caused no injuries, a statement said.
The explosive, a tube or tin which measured around 10x10cm found outside the building, "must have been placed" there, say investigators in the province of North Holland.
The incident comes shortly before national elections on March 17 widely seen as a referendum on the government's handling of the pandemic.
Prime Minister Mark Rutte's conservative VVD Party is likely to remain the largest, according to opinion polls.
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Police spokesman Menno Hartenberg said the explosive "must have been placed".
He said: "We don't know yet exactly what exploded, the explosives experts must first investigate.
"What we're saying is that something like that doesn't just happen by accident, it has to be laid."
No arrests have been made.
The area has been cordoned off by police with the Explosives Ordnance Disposal Service (EOD) on its way, local media reports.
All appointments at the site have been called off until at least tomorrow and it remains unknown when the street will re-open.
The GGD-GHOR Nederland-run centre, in Middenweg 7, which opened at the end of November, can perform up to 800 tests per day.
In a tweet, police said: "At the test street Covid of the GGD in Bovenkarspel, an explosive went off this morning at 6.55 am. Windows destroyed, no injuries. Police are investigating. Environment is cordoned off."
The region around Bovenkarspel, a rural town, is currently suffering one of the Netherlands' worst Covid-19 outbreaks, with 181 cases per 100,000 inhabitants, compared with around 27 per 100,000 nationally.
At least one hospital has been forced to send patients to other provinces due to lack of space in its intensive care units.
At the end of January a fire was started on a street in Urk housing a test centre during riots around curfew, with three people subsequently arrested.
At the start of last month, fireworks were found next to combustible materials near another test site in Hilversum and towards the end of 2020 a centre in Breda was vandalised.
Today marks the first day in several months in which lockdown measures in the Netherlands have been slightly eased, with hairdressers reopening and non-essential stores allowed to accept a small number of visitors by appointment.
A night-time curfew from 9pm to 4.30am remains in place.
Anger against the country's healthcare authorities has increased since the start of 2021 and the head of the country's National Institute for Health is now accompanied by a security detail to public appearances.
A security guard was inside the testing centre when the explosive went off, but was not injured, national broadcaster NOS reported.
