Explosion in northern town, which caused damage but no injuries, comes after riots over lockdown measures.
Dutch police say a coronavirus testing centre in the northern Netherlands was intentionally targeted, after an explosion at the site.
The blast in Bovenkarspel early on Wednesday morning shattered windows but caused no injuries, police from the province of North Holland said in a statement.
The explosive “must have been placed” there, police spokesman Menno Hartenberg told Reuters news agency.
Hartenberg said that “something metal” had caused the blast.
“We don’t know yet exactly what exploded, the explosives experts must first investigate,” he added.
Officers have cordoned off the area as they carry out investigations, public broadcaster NOS reported.
All Wednesday morning test appointments in Bovenkarspel have also been cancelled, according to NOS.
The blast follows the worst unrest the Netherlands has witnessed in decades, with many angered by strict restrictions aimed at containing the COVID-19 pandemic.
Earlier this year, the government introduced a night-time curfew, the first to be implemented in the Netherlands since World War II.
The measure went into effect on January 23 and led to several days of rioting.
The protests gripped several cities and saw rioters torch a COVID testing centre in Urk, a northern village.
Police clamped down and hundreds of rioters were arrested. Many have already been sentenced by Dutch courts.
The curfew is in effect from 9pm to 4:30am daily, and is due to expire on March 15 – two days before general elections.
Prime Minister Mark Rutte’s government won a court case last week over its use of emergency powers to install the measure.
The curfew is part of a strict lockdown in which bars, restaurants and non-essential shops have been closed for months.