Get breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings.

CROSBY, Texas — Two explosions shook a flooded chemical plant near Houston early Thursday, sending a plume of black smoke into the air and triggering an intense fire that continued to burn.

Authorities warned that further blasts were likely to occur on site since chemicals weren't being stored at the appropriate temperatures after the facility lost power following Hurricane Harvey.

Residents in a 1.5-mile radius of the Arkema Inc. plant were first evacuated Tuesday, and the water levels there remain too dangerous for workers to assess the situation from the ground, officials added.

"That's why we want people to respect [the] radius. It's not over. This is very serious and we know that," Richard Rennard, of Arkema Group, said at a news conference.

He added that the explosions were not massive, and that the pressure building up inside the containers where the chemicals are located eventually produces a "popping sound."

The smoke that was emanating from the facility irritated the eyes and throats of more than a dozen law enforcement officers who were monitoring the scene, said Harris County Sheriff Ed Gonzalez. Some of them went to the hospital out of precaution.

"It's basically like standing over a barbecue pit or something like that, where you get smoke in your eyes," he added.

The plant in Crosby, Texas — about 20 miles northeast of Houston — was inundated by more than 40 inches of rain from Harvey and has been without electricity since Sunday.

The plant manufactures organic peroxides commonly used in everyday products like kitchen countertops, industrial paints, polystyrene cups and plates, and PVC piping. The materials must be kept very cool, otherwise there is "the potential for a chemical reaction leading to a fire and/or explosion within the site confines," Arkema said.

#Breaking Just saw plume of smoke over flooded chemical plant in Crosby, TX. Firefighters evacuating us @nbc6 pic.twitter.com/9pN8drDCcq — Julia Bagg (@JuliaNBC6) August 31, 2017

Without power or backup generators running at the site, the organic peroxides stored inside nine containers — described as 18-wheeler box vans — warmed to dangerous levels, officials said. Arkema Group, one of the world's largest chemical companies, had warned Wednesday that the plant would catch fire at some point — adding that there was nothing to stop it.

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

The fire on Thursday morning from one of the containers sent a plume of smoke about 30 to 40 feet into the air, authorities said. It was not immediately clear how long it would take for the chemicals in the remaining containers to degrade.

When asked if the fumes coming from the plant are toxic, Rennard told reporters that the smoke itself is what's potentially dangerous.

"They're noxious, certainly," he said. "I don't know the composition of the smoke."

Gonzalez also downplayed any immediate threat.

"It is not anything toxic," he said. "It is not anything that we feel is a danger to the community at all."

Brock Long, administrator for the Federal Emergency Management Agency, said at a separate news conference Thursday that evacuations are based on "plume modeling," which is used to predict the geographic extent of a hazard area from an explosion.

"By all means, the plume is incredibly dangerous," Long said of what's occurring in Crosby.

In a statement issued early Thursday, the France-based company confirmed they had been notified by authorities of the blasts at around 2 a.m. local time (3 a.m. ET).

A map showing the location of the Arkema chemical plant in Crosby, Texas. Google Maps

"We want local residents to be aware that product is stored in multiple locations on the site, and a threat of additional explosion remains," the statement said. "We have been working closely with public officials to manage the implications of this situation."

It added: "As agreed with public officials, the best course of action is to let the fire burn itself out."

The firm said it made extensive preparations for Harvey, but "the plant has never experienced flooding of this magnitude before."

Related: Hurricane Harvey Has Left Houston, but the Flooding Continues

Shawn Hawthorn, a senior firefighter for the Crosby Volunteer Fire Department, said Wednesday that the plant was difficult to reach because streets in the area were under several feet of water.

Earlier, Arkema spokeswoman Janet Smith told The Associated Press that a blaze was inevitable and any fire "will be explosive and intense in nature."

Several deputies who had been close to the plant had complained of "headaches and dizziness."

In total, 15 law enforcement officers were being observed at the hospital, Bob Royall, an assistant chief with the Harris County Fire Marshal's Office, told TODAY. They were later released.

Royall said at a news conference that the air is being monitored to try to determine where the smoke might go.

"Right now, our 1.5-mile-safety zone around this is more than adequate, and until something changes, we're going to continue our same posture," he added.

The Federal Aviation Administration closed air traffic near the site late Wednesday. The National Guard was on the scene, and the Department of Homeland Security set up a command post near the site.

The incident raises memories of the devastating explosion at a West Fertilizer Co. facility in West, Texas, in April 2013. Fifteen people were killed, and more than 160 others were injured.

Speaking before the explosions occurred, Richard Rowe, chief executive of Arkema's North America operations, said the fire at the chemical plant wasn't expected to "pose any long-term impact."

Julia Bagg reported from Crosby, Texas. Alex Johnson reported from Los Angeles and Jason Cumming reported from London.