CONYERS, Ga. -- More than 90,000 residents east of Atlanta were told to keep sheltering in place Monday a day after a chemical plant fire sent a massive plume of dark smoke high into the sky that could been seen for miles.

The haze and chemical smell had spread to Atlanta by Monday morning, prompting firefighters to use detectors to check the quality of air in various parts of the city, Mayor Andre Dickens said.

Closer to the source of the fire, officials said chlorine, a harmful irritant, had been detected in the air from the fire at the BioLab plant in Conyers, Georgia, the Rockdale County government said in statement early Monday. The plant is about 25 miles (40 kilometers) southeast of downtown Atlanta.

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

In Atlanta, officials said they believe the hazy conditions and chemical smell is "related to the BioLab fire, but why we are seeing the change in conditions is what we are attempting to figure out.”

“Latest plume modeling indicates it moving to the northeast, which it is clearly not," the Atlanta-Fulton County Emergency Management Agency said in a statement.

Emergency management officials in Fulton County, which encompasses much of Atlanta, said people with concerns about the haze or smell should stay indoors, close their windows and doors and turn off the air conditioning.

The fire was brought under control around 4 p.m. Sunday, officials said.

Interstate 20, which was shut down in both directions in the area Sunday, was reopened Monday morning, officials said. Some other roads in the county and county government offices were closed.

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 around 5 a.m. Sunday 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.

McDaniel said 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.

The company also said that no injuries were reported.

“Our top priority is ensuring the community’s safety, and our teams are working around-the-clock to respond to the ongoing situation at our facility in Conyers, Georgia," a spokesperson said in a statement Monday. "We continue to work collaboratively with first responders and local authorities and have deployed specialized teams from out of state to the site to bolster and support their efforts. We are all focused on remediating the situation as rapidly as possible.”

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