Essex Fire and Rescue service said that the fire is now being scaled down.
Area Manager Dave Bond said: “This is a significant fire but we have it under control and there is no wider risk to members of the public. A number of industrial units have caught alight as well as a field and crews have been working to prevent the fire spreading to nearby houses.
“While on the scene, fertiliser inside one of the units exploded and residents across the county have reported hearing and feeling it. This is why we declared a major incident and I want to reassure our residents that there is no wider risk to the public at this time.
“Everybody at the scene is safe, residents nearby have been evacuated while we put the fire out and Southend Road is currently closed to allow us more space to work safely.
“We expect to be at the scene throughout the night. It is producing lots of smoke so we recommended keeping your windows and doors shut if you live nearby.
“Roads will remain closed. Please avoid the area.”
