A US Marine veteran has been credited with saving the lives of dozens during the Las Vegas shooting by stealing a pickup truck to carry seriously injured victims to hospital.

Taylor Winston, 29, stayed behind to help as gunman Stephen Paddock opened fire on the open-air music festival from the 32nd floor of the Mandalay Bay Hotel.

As bullets rained down on music fans, another group of friends set up an emergency triage area to treat those caught up in the deadliest ever US gun attack.