A Walmart (WMT) distribution center in Plainfield, Indiana, was still ablaze in the early morning hours Thursday as firefighters worked to extinguish the massive fire roughly 18 hours after it started.

According to WXIN, a Fox affiliate out of Indianapolis, the fire at the 1.2 million-square-foot distribution center was first reported around noon on Wednesday, but could still be seen around 5 a.m. the next day from a row of charred semis.

The building was fully engulfed in flames by the time fire authorities arrived on the scene on Wednesday, a Facebook post from Indiana’s Avon Police Department indicated.

The fire at the plant produced large amounts of smoke that could be seen for miles, according to the National Weather Service.

The huge fire caused one firefighter to suffer minor injuries. The firefighter was treated for the injuries and released back to the scene, Plainfield Fire Chief Brent Anderson said, as reported by USA Today.

It was unclear at the time of writing what caused the fire at the facility. The Bureau of Alcohol, Tobacco, Firearms and Explosives will hold an investigation, which could take weeks, Anderson said, according to USA Today.

"Right now we have no idea what may have started this [and] no reason to believe it's suspicious or anything," Anderson said.

The distribution center stocked everything from food to clothes to electronics, one employee told USA Today.

Fire officials are concerned that some items inside the facility may be toxic when burned and have warned neighboring residents to stay inside and keep their windows shut, the news outlet said.

"We are going to err on the side of caution right now," Anderson added. "We will treat everything as if it's hazardous."

About 1,000 employees worked at the distribution center. All were able to escape the plant safety as the fire broke out.

Displaced workers could get temporarily relocated to neighboring Walmart stores, WXIN said.

As of Thursday's premarket hours, shares of Walmart were trading at $144.51, down 84 cents, or 0.58%.

A Walmart logo is seen outside a store in Washington, DC, on August 18, 2020
A Walmart logo is seen outside a store in Washington, DC, on August 18, 2020 AFP / NICHOLAS KAMM