More than 90,000 residents in a county east of Atlanta, Georgia, have been told to remain sheltering in place and businesses were told to stay closed a day after a chemical plant fire sent a massive plume of dark smoke high into the sky.

Air quality surveys done by the US Environmental Protection Agency and the state Environmental Protection Division “revealed the harmful irritant chlorine” detected in the air from the fire at the BioLab plant in Conyers, Georgia, the Rockdale County government said.

The statement said: “For everyone sheltering in place, the best practice is to turn the air conditioning off and keep windows and doors shut.”

The fire was brought under control at around 4pm on Sunday (9pm BST), officials said.

The Interstate 20 road, which was shut down in both directions in the area on Sunday, was reopened on Monday morning, officials said.

Tens of thousands of people were told to shelter in place, and businesses were closed (WSB-TV via AP)

People in the northern part of Rockdale County, north of Interstate 20, were ordered to evacuate on Sunday, and others were told to shelter in place.

Sheriff’s office spokesperson Christine Nesbitt did not know the number of people evacuated, although it covered a large portion of the community of Conyers. Media reports said the number was 17,000.

The fire ignited when a sprinkler head malfunctioned early on Sunday morning at the BioLab plant in Conyers, Rockdale County Fire Chief Marian McDaniel told reporters.

The malfunction caused water to mix with a water-reactive chemical, producing a plume of chemicals.

There were employees inside the plant, but no injuries have been reported, The Atlanta Journal-Constitution reported.

BioLab’s website says it is the swimming pool and spa water care division of Lawrenceville, Georgia-based KIK Consumer Products.

Automated messages at two phone numbers for the company said to call back during business hours. An email was sent to the company Monday.

“We are actively responding to an occurrence at our facility in Conyers, Georgia,” a BioLab representative said in a statement provided to the Journal-Constitution.

“Our employees are accounted for with no injuries reported. Our team is on the scene, working with first responders and local authorities to assess and contain the situation.”

A small fire on the plant’s roof was initially contained but reignited on Sunday afternoon, authorities said.