(CNN) — A fire that started Tuesday afternoon at a recycling plant in the eastern Indiana city of Richmond was emitting toxic smoke and has forced evacuation orders for about 2,000 people as it is expected to burn for days, officials said.

Early air monitoring results are expected early Wednesday, Wayne County officials said. Plastics were among the items burning at the plant, and the smoke — a thick, black column rose from the site Tuesday — is “definitely toxic,” Indiana State Fire Marshal Steve Jones said in a news briefing.

“There is a host of different chemicals that plastics give off when they’re on fire, and it’s concerning,” Jones said Tuesday evening, adding he expects the fire to burn for days.

An evacuation order was put in place for residents within a half-mile of the fire, and authorities could change the order if the direction of the wind shifts, Jones said. Residents downwind of the evacuation zone — to the east and northeast — were being encouraged to shelter in place and bring pets indoors.

Residents who find remnants from the fire in their yards were asked to “not disturb or touch the debris.”

“It is unknown what chemicals may or may not be in the debris,” Wayne County Emergency Management Agency officials said.

Preliminary air monitoring results “should begin to return by daybreak” from US Environmental Protection Agency labs, the officials said Tuesday night, adding evacuation orders are in effect indefinitely.

The towering smoke plume and health concerns recall the inferno and draining of hazardous materials sparked by a freight train derailment and fire this year in East Palestine, Ohio. High levels of some chemicals recorded during that disaster could pose long-term risks, researchers have said.

The cause of the Indiana fire wasn’t immediately known and likely won’t be known until after the fire has been extinguished, officials said.

Firefighters responded to the recycling facility Tuesday to find a semi-trailer behind one of the plant’s buildings engulfed in flames, Richmond Fire Chief Tim Brown said. The trailer was loaded with an “unknown type of plastics,” and the fire spread to other piles of plastics around the trailer and eventually to the building, Brown said.

Details about what started the fire at the semi-trailer weren’t immediately available.

The evacuation order affected about 2,000 residents, the Wayne County Emergency Management Agency told CNN. Officials said they are waiting on air monitoring testing results to help decide the duration of the evacuation orders.

“We do not expect the evacuation order to be lifted tonight,” Richmond Mayor Dave Snow said Tuesday. “A bus will remain in place if needed and shelters are ready to accept citizens from the area.”

The massive blaze prompted the Richmond Community School District to cancel all classes Wednesday, with officials encouraging faculty and staff to follow shelter-in-place orders and saying there will be no online classes.

“It’s a big enough fire that it’s just not gonna be tonight,” Jones said. “It’s going to burn a while.”

The Environmental Protection Agency and the Indiana Department of Environmental Management were on site “evaluating any potential hazards resulting from the fire,” Snow said in a Facebook post.

Firefighters had trouble getting access to the facility, with piles of plastic blocking access roads, Brown said. “It creates quite a challenge because we only have access to one side of the building,” he added.

“Once the fire got out of control, it darkened down on us, (and) we backed out real quick and then went into defensive mode,” Brown said.

The flames spread to several buildings at the site, but crews managed to stop the fire’s spread before it could jump into residential areas, Brown said.

“It’s probably the largest fire I’ve seen in my career,” Brown said.

One firefighter was injured after falling and hurting his ankle and has since been treated and released from a hospital, Brown said.

No other injuries were reported. Everyone who was said to be working at the building when crews responded to the scene has been accounted for, he said.

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