South Western Ambulance Service said it was responding to a "serious incident", according to Sky News.
Fire crews were called at 11:22 am and confirmed there have been multiple casualties following a "large explosion".
A statement from Avon Fire and Rescue said: "Crews from Avonmouth, Southmead, Yate, Patchway, Kingswood and Temple are currently attending. We can confirm there are multiple casualties on site.
"We are joined by Avon and Somerset Police and the ambulance service on site. The incident is ongoing."
MAH/PR