12 fire engines are at the unit in Rectory Road, having come from across Essex, as well as London and Kent.
An HGV is understood to be alight and fire crews are attempting to surround and tackle the blaze.
An aerial ladder platform is also being used to pour water on the fire from above.
Emergency services were first alerted to the blaze at around 2.30pm today, with the smoke visible from miles away.
Police say they have closed roads in the area and people who live nearby are being advised to shut their windows.
We’re on the scene of a large fire on Blockhouse Road, #Grays.
We are assisting colleagues from @ECFRS by closing nearby roads.
Please avoid the area and expect delays on the #A126 near Cement Block Cottages.
The road is closed at the Dock Road roundabout w/ Rectory Road. pic.twitter.com/K3qYS3s1He
— Essex Police (@EssexPoliceUK) April 23, 2019
More to follow.Tags: Grays, Thurrock
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