At least four people are dead following a pile-up crash involving dozens of vehicles in Colorado that occurred as high winds blew dirt, making for low to zero visibility, authorities said.

The incident occurred around 10 a.m. local time Tuesday on northbound I-25 near Pueblo, which is about 40 miles south of Colorado Springs, authorities said. 

Over 30 vehicles, including multiple semis, were involved in the crash, according to Colorado State Patrol. Pickups pulling horse trailers, SUVs and passenger vehicles were also involved, according to Maj. Brian Lyons with Colorado State Patrol.

The pile-up occurred during “adverse weather conditions,” Lyons said, with heavy winds blowing dirt and causing “brownout” conditions.

“Visibility was next to nothing,” Lyons said during a press briefing Tuesday.

There are four confirmed fatalities in separate vehicles, Lyons said. Colorado State Patrol was working with the Pueblo County Coroner’s Office to identify the victims, he said.

Another 29 people were transported to area hospitals, Colorado State Patrol said. Their injuries ranged from minor to serious, though not all conditions were known in the wake of the crash, according to Lyons.

Authorities were working to account for everyone in the vehicles involved in the crash, as well as livestock — possibly goats or sheep — that were being transported in a horse trailer, Lyons said.

Another crash occurred on southbound I-25 involving a semi that was also caused by “significant dirt that was blowing across the highway,” Lyons said.

I-25 is closed in both directions near the scene of the crash, with the northbound side expected to remain closed for several hours as crews work to clear vehicles, Lyons said.

“Due to low visibility, drivers are urged to delay traveling until conditions improve,” Colorado State Patrol said. “If travel is necessary, avoid I-25 in this area, use caution, and reduce speed.”

High wind warnings are in effect for the region on Tuesday. The National Weather Service in Pueblo warned that “significant blowing dust” is possible on the plains, where gusts could be up to 65 mph. Mountain areas could see gusts of at least 85 mph, it said.