Fire groups and paramedics saved two individuals who were caught in the Charles Street working after the impact right away before 18.00 BST.
Lancashire Police said various individuals were likewise treated at the scene and prompted individuals to keep away from the range.
The states of the harmed is not yet known.
Occupants of Charles Street and Milbourne Street, which runs parallel to it, have been cleared by police.
A security cordon has been set up and streets in the territory have been shut.
Police prompted individuals influenced by the departure to look for shield at St John’s Church on Church Street or the Salvation Army fortress on Raikes Parade.