Explosion in northern town, which caused damage but no injuries, comes after riots over lockdown measures.
Police have used water cannon and batons to disperse a crowd of several thousand anti-lockdown protesters gathered at a field in the centre of The Hague a day before elections in the Netherlands.
The demonstration was broken up after the protesters flouted social distancing rules and ignored police warnings to disperse. Local media said several arrests were made during the clashes. There were no immediate reports of injuries.
The Netherlands has been under a tough lockdown since late January with gatherings of more than two people banned, restaurants and bars shut and with the first night-time curfew since World War II.
Dutch authorities had on Sunday stopped train services to The Hague, the seat of government, to prevent more protesters from arriving. Police initially told people to go home and announced over loudspeakers that the event was over and warned they would break up the protest by force if necessary.
Before the protest was dispersed, several people carried a homemade banner emblazoned with the text in Dutch “Love & Freedom: No Dictatorship”. Many in the crowd, gathered at the central Maliveld field in the city, were holding yellow umbrellas in a show of opposition and chanted “love, freedom, stop dictatorship”.
One demonstrator carted a makeshift set of stocks with a photo of Prime Minister Mark Rutte’s head stuck in the middle and a sign saying: “If you love the Netherlands, vote them out.”
Voting in the election will start on Monday, with polls open for three days to help ensure social distancing at polling stations. Rutte’s conservative VVD Party appears set to get a new four-year mandate.
A majority of voters reluctantly support the lockdown, given the Netherlands’ current coronavirus infection rate which is towards the high end of Europe’s range.
But the curfew, which has been extended until the end of March, prompted several days of rioting across the country when it was first imposed on January 23.
In recent weeks, smaller demonstrations have happened in Amsterdam, with riot police repeatedly called in to shepherd away protesters who refuse to leave.
They reflect a growing impatience among a small section of society at the lockdown that has seen businesses including bars, restaurants and museums shut down since mid-October.
The country of 17 million has registered more than 1.1 million COVID-19 cases and more than 16,000 deaths in the pandemic.