DIVERNON, Ill. >> Winds stirred up a wall of dust from farm fields that engulfed a stretch of busy interstate highway in a matter of minutes. The brown cloud’s intensity caked even the insides of vehicles in dirt. As darkness enveloped them, some cars and trucks hurtling down the road put on their brakes; others didn’t.

They slammed into one another, leaving them mangled or in some cases burned. And when it was over, almost 40 people were injured and seven people were dead — at least two of them still unidentifiable.

Monday’s deadly and fiery crashes along a 2-mile stretch of Interstate 55 in central Illinois, 75 miles (120 kilometers) north of St. Louis and just south of the state capital of Springfield, came as high spring winds kicked up dust at a time when farmers are busy tilling or planting their fields, police said.

“They were very unusual circumstances. Certainly dust storms happen, but it is not something that happens every day here in this part of Illinois or any part of Illinois,” Illinois State Police Director Brendan Kelly said at a news conference Tuesday.

Illinois State Police raised the death toll to seven later Tuesday.

“Initially, six individuals were found deceased at the crash scene. However, the severity of the crash masked the remains, and what was previously believed to be the remains of one individual was two,” police said in a news release.

The highway was closed in both directions after the late-morning crashes on Monday, a scene Gov. J.B. Pritzker described as “horrific.”

Northbound and southbound lanes reopened around 6 a.m. Tuesday, Kelly said, before state police closed the same 20-mile section of road again late Tuesday afternoon as nasty winds continued. The traffic advisory indicated there had been no accidents but the action was taken as a precaution. The section reopened later Tuesday afternoon.

Earlier, Kelly had said it was extremely rare to close a highway due to weather except in blizzard conditions. Noting three memorable dust storms in the same region since 1983, the National Weather Service reported that one, in 1990, resulted in closure of an 18-mile section of Interstate 57.

Monday’s crashes involved 40 to 60 cars, along with tractor-trailers, two of which caught fire, state police said. The six people who died were all in northbound lanes, while 37 people on both sides of I-55 were taken to hospitals.

Witnesses described a sudden burst of dirt completely erasing visibility — “It was like a white out, only it was a brown out,” said Evan Anderson, 25, who was returning home to St. Louis from Chicago.

Caught between two semis, Anderson said he believes he was spared serious injury because the truck behind him turned slightly before striking his vehicle.

“People tried to slow down, and other people didn’t, and I just got plowed into,” Anderson said. “There were just so many cars and semitrucks with so much momentum behind them.”

Those hurt in the crash range in age from 2 to 80 and have injuries from minor to life-threatening, police said. One of the six people killed was Shirley Harper, 88, of Franklin, Wisconsin, police said.

Two of the six people killed remain unidentified, Kelly said, and state police were seeking tips from the public about their identity. One victim was driving a blue Chrysler 300, and the other was in a Hyundai, its color unknown. He said they were both adults but would not reveal their genders or other details.

More than 40 troopers were sent to the scene, including members of the state police traffic crash reconstruction team, Kelly said. Those investigators are very early in their inquiry and have a lot of evidence to review and people to interview as part of their probe.

“We have a lot of science that has to be done to see what we can determine,” Kelly said.

Winds were gusting between 35 and 45 mph (56 and 74 kph), the National Weather Service said. Meteorologist Chuck Schaffer said the area where the crashes occurred is “very flat, very few trees.”

Farmers in central Illinois, including Montgomery County, where the crashes occurred, are tilling fields and planting corn and soybeans, the region’s chief crops, said Emerson Nafziger, a professor emeritus in the Department of Crop Sciences at the University of Illinois’ Urbana-Champaign campus.

Much of central Illinois has received little rain in recent weeks, he said, and cropland that is normally wet this time of the year is dry — and with farmers active in their fields, high winds can easily send dust airborne.

“It just has to dry the top surface, a quarter-inch of soil, and then there’s a huge amount to blow around,” Nafziger said. “In this case, a lot of fields have been tilled, some have been planted, but the tillage process and even spreading fertilizer will put up a fair amount of dust.”

Illinois ranks 26th among the states in terms of farm fields planted without tillage. Tilling aerates the soil, controls for weeds and pests and prepares the land for seed germination, but can increase soil erosion — including by the wind.

According to the U.S. Department of Agriculture’s 2017 Land Use Practices Census, 29% of Prairie State cropland was no-till. Illinois’ 22.2 million acres (898,000 hectares) of land in production ranks it 4th in the nation.

Kelly said his investigators would try to determine whether nature was the only factor. State Police Division of Criminal Investigation officers responded initially to identify bodies and contact family members, but while their work continues, Kelly downplayed the notion of criminal charges and would not speculate on what they could be.

“It does not benefit a farmer to lose a bunch of topsoil, so they have no motivation to do something that would cause this,” Kelly said. “There’s no logic to saying that someone did this on purpose and they were somehow skirting some sort of regulation, but we’re going to … follow the facts wherever they take us.”

Tom Thomas, 43, who was traveling south to St. Louis before Monday’s crashes, said after the vehicle he was in got into a crash, the only thing he could hear “was crash after crash after crash behind us.”

Dairon Socarras Quintero, 32, who was driving to St. Louis to make deliveries for his custom frame company based in Elk Grove Village, said after his truck hit the vehicle in front of him, he exited and moved to the side of the road, then returned after the chain reaction of crashes ended behind him. Socarras Quintero said the dust continued to blow ferociously as he checked on other motorists and emergency crews arrived.

He held up his backpack, which was caked with dust even though it was inside a closed truck cab.

———

Associated Press reporters Rick Callahan and Ken Kusmer in Indianapolis, and Ed White in Detroit contributed to this report.