As many as five law enforcement agents were hurt when an explosive device unexpectedly detonated during a training exercise at a Montgomery County prison.

Several emergency vehicles, including at least two fire trucks, swarmed a large field near SCI - Phoenix state prison in Skippack Township just after 11 a.m. Thursday.

The training was being conducted by the Montgomery County bomb squad.

A spokesperson from the Federal Bureau of Investigation (FBI) said three members of the Montgomery County Sherif's Office, a Pennsylvania State Trooper, and an FBI agent were hurt in the blast, Fox 29.

Officials said in a Friday afternoon update that the injuries are not life-threatening, but they "vary and some are significant."