A 12-year-old boy was critically injured Monday evening when an illegal firework exploded in his hands at a playground in the city’s Summerdale section, police said.

Police and medics were called to the Houseman Playground at Summerdale and Godfrey Avenues for a reported explosion and found the boy wounded next to the basketball court, said Chief Inspector Scott Small.

The boy, whose name was not released, had lost a finger on one hand and had severe injuries to the palm and knuckles of his other hand, Small said. He was taken by medics to Einstein Medical Center where he was listed in critical condition. The injuries were not life-threatening, Small said.

A preliminary determination by the police Bomb Squad was that the device was an illegal explosive device with the explosive power of a quarter- or half-stick of dynamite, Small said. There were dozens of people nearby but no one else was injured.