Police advised residents to keep their doors and windows closed as fire crews dealt with a chemical spill.
Five crews - two from Maldon and one each from Witham, Chelmsford and Colchester - were called to Arla Foods, in Bury Lane, Hatfield Peverel, at 10.30pm yesterday.
An Essex Fire and Rescue spokesman said: "A 200 metre exclusion zone was put in place and residents in the area were advised by police to keep their doors and windows closed as crews worked to deal with a chemical spillage.
"No one was evacuated and there were no casualties.
"Crews were called to Arla Foods after workmen reported chemical vapours spilling from a bulk storage container.
"The tank contained hydrochloric acid and staff on site wearing respiritory equipment were withdrawn from the building for their safety by crews arriving at the scene.
"Firefighters set up a decontamination zone so that they could redirect the acid by operating a valve on its tank. They donned gas tight suits to carry out the operation."
The area was made safe shortly before 2am, and the site was left in the care of factory staff and the Environment Agency.