The police will be carrying out extra surveillance in the near future after several incidents in the Lombardijen district of Rotterdam.
On Saturday evening, another fireworks bomb exploded in a municipal building on Dantestraat.
No one was injured, but residents of apartments above had to leave their homes.
The fire brigade quickly got the fire under control.
Shortly afterwards, around 2:30 in the morning, a van from the municipality of Rotterdam caught fire on the Moliereweg after a firework bomb.
Saturday evening and night was also hit at other places in the Rotterdam district.
Heavy fireworks exploded near a house on Horatiusstraat, causing great havoc.
Fireworks were thrown through a letterbox at a house on the Ogiersingel.
Three men in dark clothes then ran away.
On New Year's Eve, a fire started after fireworks had been set off at two schools on Catullusweg.
It is still unclear whether there is a connection between all these incidents.
The leader of the police investigation calls it "really bizarre and unacceptable".
"Fortunately, no one was injured in all these incidents, but you shouldn't think about what could have happened."
Camera images from the neighborhood are currently being investigated.
The police say they will be carrying out stricter surveillance in Lombardy in the coming period, recognizable and in plain clothes.
Mobile cameras are also used for surveillance.
The police are calling on witnesses to report.