The incident happened at 10.20am when the crew from Blaenavon were responding to a call.
Five crew members were injured. It's thought it took around two hours to free the most seriously injured firefighter from the scene.
He's been taken to the University Hospital of Wales in Cardiff complaining of neck injuries and a possible broken leg.
Three other firefighters were taken to Nevill Hall hospital with back injuries. The fifth injured firefighter was allowed to leave the scene.The road has been closed for most of the day as police investigate what happened.