There have been 358 explosions outside private homes and business premises so far this year, compared with just 227 in 2022 as a whole, broadcaster NOS said on Wednesday, quoting police figures.

More than half the blasts took place in Amsterdam and Rotterdam, but more rural areas are increasingly being affected. In Groningen, for example, a hairdressers’ salon has twice been targeted while in Oude Pekela and Winschoten there were  explosions outside businesses on Tuesday night.

Criminologist Jasper van der Kemp told NOS that copycat behaviour is playing a role in the trend. “It is a relatively easy way to spread fear,” he said. If you have a dispute with someone, setting off a firework is a way of showing you know where they are, he said.

Earlier research in Rotterdam suggested the home made bombs, often using fireworks, are usually placed by teenagers, and a quarter of them are under the age of 18.

Although drugs gangs are behind most of the explosions, the habit is also moving into more mundane disputes, Kemp said. “It can also be people who have just had a fight and who happen to have a firework to hand,” he said.

The fact that the explosions are carried out at night shows that “criminals want to send a message” rather than cause injury, police chiefs told Nu.nl in May.