The fire service said the cause of the fire was currently unknown.
Crews from Avonmouth, Patchway, Southmead, Nailsea, Temple, Pill, Portishead, Kingswood, Chew Magna, Clevedon, Bedminster, Yate, Thornbury and Weston-super-Mare have attended the incident.
The fire service said: “We’re responding to a significant fire at a recycling centre on Kings Weston Lane, Avonmouth. A major incident has been declared.
“Residents and businesses nearby should stay indoors and keep windows and doors closed where possible due to smoke in the air,” it said.