At least one person was swept downstream by swift currents Saturday after a pickup truck collided with an oncoming vehicle before plunging into the North Fork of the Payette River in southwest Idaho.

Investigators say additional occupants may still be inside the submerged pickup but dangerous river conditions are preventing rescuers from reaching the vehicle.

The crash occurred just before 3 p.m. on State Highway 55 during a period of heavy weekend traffic north of Cascade, about 65 miles north of Boise. According to the Idaho State Police, a southbound green Dodge Ram crossed into the northbound lane, collided with another vehicle and then left the roadway and entered the river.

Witnesses reported seeing at least one occupant exit the truck and be carried downstream by the current. Additional witness accounts suggested there may have been other people inside the pickup at the time of the crash — but with the truck submerged and river conditions hazardous, the total number of occupants has not been confirmed.

Swift water rescue teams, law enforcement, fire and emergency medical personnel from multiple agencies responded and conducted search operations along the river corridor. Despite their efforts, high water levels and dangerous currents prevented responders from safely reaching the submerged pickup.

"The swift current, high water levels, and challenging conditions have made this a complex response involving specialized rescue resources," said state police trooper Richard Knapp. "Our focus remains on locating and identifying anyone involved, safely recovering the vehicle, and determining exactly what occurred."

The truck will remain in the river until conditions allow for safe recovery. Officials said operations may include drawing down the river's water level, potentially as early as Monday.

The three occupants of the second vehicle sustained minor injuries and were treated and released at the scene.

Highway 55 was shut down for several hours because of the accident.

The crash remains under investigation. Anyone who witnessed the incident is asked to contact state police at 208-846-7500.

Anyone who has been unable to reach family members or loved ones who were traveling through the area Saturday afternoon is also urged to call state police.