Merseyside police have begun an investigation after industrial fireworks exploded in seven telephone kiosks in Liverpool.
No-one is believed to have been injured in the blasts, which happened on Friday night.
Police say the offenders have put the lives of innocent people at risk and officers are using all their resources to catch them.
An operation using CCTV cameras and extra police patrols has begun to tackle the problem.
Police are also urging people using phone kiosks to be extra vigilant and to report anything suspicious.
The force has condemned those responsible for what it calls this "dangerous and mindless activity".
It says the offences will be treated seriously by the police and the courts.