A “criminal network” is behind the organised fireworks attacks on police, firefighters and emergency services on New Year’s Eve, national police chief Janny Knol said on television talk show Pauw en De Wit.

In Floradorp in Amsterdam-Noord, police were pelted with fireworks shot from a device resembling a machine gun. “The materials for this were bought for this purpose,” Knol told the programme.

No arrests have been made for the attack in Floradorp and the investigation is ongoing, she said. “We want a complete case. We are not only looking for the culprits themselves but those who were involved in the background. To me, this is a criminal network,” Knol said.

A group commander from Utrecht who was also a guest on the show said he and his team had been ambushed when their van was forced to stop by a car blocking their way near a school.

“A group of around 30 or 40 youngsters were waiting there, throwing fireworks at us. We were lucky it was legal fireworks … or things could have ended very differently,” he said.

Rioters also torched cars, pelting the firefighters called to the scene with fireworks.

Police arrested some 250 people during what officers described as a violent New Year’s Eve, marked by widespread disorder, targeted attacks on emergency workers and a sharp rise in fires and emergency calls. More arrests are expected, based on numerous videos of attacks on police.

At least two people died and others – including many children – were seriously injured in incidents involving fireworks in what was the last year before all but the lightest sort are banned from sale to consumers.