1114 GMT April 21, 2021
The early morning blast in the town of Bovenkarspel, 60 kilometers (40 miles) north of the capital Amsterdam, was caused by a metal cylinder left outside the building, police said, AFP reported.
The incident comes weeks after another testing center was burned down during violent riots across the Netherlands against a coronavirus curfew.
"Police were called at 6.55 a.m. by a security guard from the corona test center to say that an explosion had taken place. He had heard a loud bang and then saw that several windows of the building had broken," a police statement said.
"Outside the building was a metal cylinder that had exploded. No one was injured in the incident."
North Holland police spokesman Menno Hartenberg 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 center," Hartenberg said.
"We are not ruling anything out and can't say anything about a motive, an investigation is underway."
Hartenberg added: "It was a metal object somewhere between a tube and a canister."
Police forensics officers in white overalls were conducting a fingertip search of the area, which was cordoned off.
Dutch Health Minister Hugo de Jonge condemned the attack, saying 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," de Jonge said on Twitter.
The Dutch GGD public health department said it was "horrified" by the "aggressive and intimidating" incident.
"Our people must be able to do this crucial work safely. This cowardly act of destruction affects us all," GGD national president Andre Rouvoet said on Twitter.
A bomb squad was sent to determine whether any explosive material remained at the scene, public television network NOS reported.
The part of the Netherlands in which Bovenkarspel is located is currently suffering one of the country's most serious outbreaks, with 81 infections per 100,000 inhabitants, compared to a national average of 27.2, NOS said.
The Netherlands has recorded more than one million coronavirus cases since the start of the pandemic and over 15,000 deaths.
Some 1.3 million people have received at least one dose of vaccine.
In January a COVID-19 testing center was set on fire in the conservative protestant fishing village of Urk as protests broke out over the start of an overnight curfew in the Netherlands.
The Netherlands suffered several nights of rioting, the most violent the country has seen in decades.
The blast in Bovenkarspel came as the Dutch government on Wednesday began easing its toughest anti-virus measures since the pandemic began, ahead of elections in two weeks.
Anger over the COVID measures has been growing in the Netherlands, as well as support for conspiracy theories about the virus.