A truck transporting around 100 monkeys to a lab collided with a dump truck off of Interstate 80 in Pennsylvania on Friday, setting four monkeys loose — one of which is still unaccounted for.

The crash occurred in Montour County, according to the Associated Press, and residents are urged to neither look for the cynomolgus monkey nor attempt to catch it if they come into contact with it, Pennsylvania State Troopers tweeted. Instead, citizens should call 911 immediately if they encounter the primate.

Pennsylvania State Police say the crash happened around 3:30 p.m. Friday on “Route 54 just off Interstate 80 near Danville,” WNEP reports. The collision set four monkeys loose, and Route 54 was temporarily closed before it reopened later in the evening, according to WBRE/WYOU.

Crates were littered across the highway as troopers brandishing rifles scoured the area for the primates, the Associated Press reports.

According to the outlet:

The truck had been on its way to a lab, Trooper Andrea Pelachick told The Daily Item newspaper of Sunbury.

The location of the lab and the type of research for which the monkeys were destined weren’t clear, but cynomolgus monkeys are often used in medical studies. A paper posted on the website of the National Center for Biotechnology Information referred to them as the most widely used primate in preclinical toxicology studies.

Trooper Laura Lesher said state police secured the scene for the Pennsylvania Department of Health and the U.S. Centers for Disease Control and Prevention.

The search for the three-pound monkeys was headed by the Pennsylvania Game Commission with the assistance of the state police, which provided a helicopter for search efforts, according to WBRE/WYOU.

WNEP reports that troopers found a monkey in a tree just prior to 7:00 p.m.

“We later heard three shots ring out. It’s unclear what type of weapon was used and we’re not sure where the monkey is or its condition,” the outlet reports.

Investigators reportedly left the scene shortly after the shots were fired.

It was neither clear where the remaining monkeys were located, nor was their status clear, according to the Associated Press. Similarly, the drivers’ condition was not clear.