Avon Fire and Rescue Service has told the BBC there have been "multiple casualties" although they couldn’t say exactly how many.
They also confirmed the explosion was at a "water waste treatment works in Avonmouth".
A statement from Avon Fire and Rescue said:
"We have been called to a large explosion at 11:22 in a warehouse in Avonmouth on Kings Weston Lane.
"Crews from Avonmouth, Southmead, Yate, Patchway, Kingswood and Temple are currently attending.
"We are joined by Avon and Somerset Police and Ambulance on site.
"The incident is ongoing."
Emergency services are currently near the Avonmouth warehouse following an explosion.Here are the latest pictures from the scene.Copyright: BBCCopyright: BBCCopyright: BBCCopyright: BBC