Essex Fire and Rescue has confirmed an explosion and leak of caustic soda in Thurrock.
It happened at a chlorine scrubbing unit on Oliver Road and Stoneness Road. Five fire engines are on the scene.
One man has received medical treatment, but his injuries are not thought to be life threatening.
More top news
A genetic disorder meant Fabiana and Paula Chávez lost their sight as teenagers. They are now pianists, music researchers and educators.
On Tuesday morning, the group's co-founder, Gail Bradbrook, was filmed climbing the entrance to the Department for Transport in Westminster.
Extinction Rebellion activists have brought disruption to the City of London as the number of arrests topped 1,400 over a week of protests.