UPDATE from Essex Fire an Rescue:

Neil Fenwick  Area Manager at Essex County Fire and Rescue Service, is currently at the scene and has said: “We understand that the cloud includes an amount of hydrochloric acid.

“A 100 metre exclusion zone was created at the site earlier today as a precautionary measure.

“We now know that these fumes were caused by a tank that has failed, the leak is contained to within the site.

“Firefighters are now safely managing the leak and this process is expected to continue for some time.

“Six crews took over the incident at 8.30pm from the crews who initially attended.

“Emergency services are working hard to make the site safe again as soon as possible. Thank you for your patience. Road closures around the site continue to remain in place.

“If you live nearby, the advice is that you should stay inside and keep all windows and doors closed.”

Health advice: Please keep doors and windows closed if you live nearby. If you’re in a car or lorry in the area, keep your air conditioning turned off. If you have existing respiratory problems, keep medication with you and if you feel unwell call 111.