The missile exploded at the paramedics' feet, causing burns to their uniforms, as they responded to an emergency call at the club in the Trevor Hill area just after 1am on Sunday.
A spokesman for the NI Ambulance Service (NIAS) said that the crew was shocked by the incident, and experienced slight hearing distortion.
They continued to treat the patient, who had sustained a leg injury, before transferring him to Daisy Hill Hospital.
The NIAS spokesman said that it was of particular concern that the incident occurred in such a confined space, increasing the potential for more serious injury to the crew and others present.
"NIAS paramedics have witnessed at first hand the devastating impact of fireworks injuries," he said.
This person was reckless with the lives of our staff and others in the immediate vicinity. That no-one was seriously injured is a result of nothing more than good fortune.
Northern Ireland Ambulance Service
He said the incident had a knock on impact on the Newry area as the crew were unavailable to respond to further calls immediately after the incident as they were required to make statements to the police.
"Their temporary unavailability had the potential to impact negatively on our response to life threatening emergency calls, the fault for which lies, quite clearly, with the individual who was responsible for this incident," the spokesman said.
The accused has been charged with two counts of common assault, two counts of criminal damage, possession of an offensive weapon and disorderly behaviour.
He is expected to appear before Newry Magistrates' Court on Monday morning.