More than 4.5 million people, including reality TV star Kim Kardashian, called for a reduction in Rogel Aguilera-Mederos' punishment, which the judge handing it down noted was the result of mandatory sentencing rules in the US state of Colorado.

Aguilera-Mederos, a Cuban immigrant, was transporting timber in April 2019 when his brakes failed on a downhill stretch, and he did not use an emergency exit ramp.

His out-of-control truck plowed into traffic, killing four people and injuring several others.

Aguilera-Mederos was found guilty by a jury on 27 counts including multiple vehicular homicides, and a judge handed down a 110-year sentence, which he said was the mandatory minimum under Colorado law.

Colorado Governor Jared Polis on Thursday acted to cut what he said was an "arbitrary and unjust" outcome.

"The length of your 110-year sentence is simply not commensurate with your actions, nor with penalties handed down to others for similar crimes," he wrote in a letter to Aguilera-Mederos.

"There is an urgency to remedy this unjust sentence and restore confidence in the uniformity and fairness of our criminal justice system, and consequently I have chosen to commute your sentence now."

Aguilera-Mederos will be eligible to apply for parole in five years.