The sequence began when three deputies stopped to assist a semitrailer on the eastbound side of the highway. As they worked, a passing car struck the deputies' parked vehicles, according to the Clear Creek County Sheriff's Office. The impact set off a second collision involving four additional vehicles and a second semitrailer.

Two of the three deputies were injured and transported for treatment. Six people from the civilian vehicles were also hospitalized. The severity of their injuries was not immediately disclosed, and officials did not release the names or conditions of those hurt.

The eastbound lanes were shut down while emergency crews responded and investigators worked the scene, backing up traffic through the I-70 mountain corridor west of Denver. The highway is the primary route between the metro area and the ski resorts and mountain communities of Summit and Eagle counties, and even brief closures can strand drivers for miles.

The crash highlights the hazards deputies and other first responders face when they pull onto the shoulder to help stranded motorists. Colorado's move-over law requires drivers to shift lanes or slow down when approaching emergency vehicles stopped on the roadside, a rule state officials have repeatedly promoted as a safeguard for law enforcement, tow operators and highway workers.

Investigators have not said whether speed, weather or distraction contributed to the initial strike. The Clear Creek County Sheriff's Office is leading the investigation, and no citations had been announced as of Thursday evening.

Anyone who witnessed the crash or has information about the passing vehicle is asked to contact the Clear Creek County Sheriff's Office.