KALISPELL, Mont. — Smoke from a controlled burn along Interstate 15 in northern Montana obscured the vision of drivers, leading to a chain reaction crash that killed two people and injured four others, the Montana Highway Patrol said.

The crash happened at about 1:15 p.m. Monday near Conrad when the driver of a semitrailer slowed down to 25 mph when smoke obstructed his vision, the patrol said. The truck was rear-ended by another semitrailer, which in turn was rear-ended by a car carrying the victims.

A small sport utility vehicle hit the back of the victims’ car.

The crash killed a 20-year-old woman and a 17-year-old girl from Columbia Falls, the Daily Inter Lake reported. Their names have not been released. It was not clear who was driving, the patrol said.

A 51-year-old man from Canada who was driving the second truck was injured along with three Colorado residents in the SUV.