An armed bystander has been hailed as a hero after firing at a gunman during a shooting at an In-N-Out Burger restaurant in southern Idaho, with law enforcement saying it diverted the gunman and saved lives.

Jordan Salinas, 35, a healthcare worker, was identified as the man who fired at the gunman by the Idaho Statesman on Sunday.

He told the newspaper that after pulling into the restaurant’s parking lot with his girlfriend on Saturday afternoon, he saw people fleeing through the doors.

He heard the sound of gunfire and ran towards it with his semi-automatic pistol drawn. Once he located the gunman standing by the drive-thru window and firing at cars, he fired his pistol.

Salinas told the newspaper that he felt “no fear” as he ran towards gunfire. “There’s a task that needs to be done, and we’re the ones who need to do it,” he said.

The shooting left four people dead, including the gunman, and seven others injured. The gunman, identified as 24-year-old Chad Williams, died from a self-inflicted gunshot wound, police said.

At a news conference on Sunday, Twin Falls County Sheriff Jack Johnson said a bystander and an off-duty state trooper had exchanged gunfire with the gunman, forcing him to take cover.

"I want to extend my deepest thanks to the off-duty trooper and the good citizen that engaged the shooter,” Johnson said.“These people are true heroes in our community, and their actions diverted the shooter, and no doubt saved many lives.”

In a post on Facebook on Sunday, Salinas thanked those who have reached out to him with messages of support.

“In the coming days, I'll share a more complete account of what happened, to the best of my recollection, when I'm able,” he wrote.

“For now, my heart remains with the victims, their families, and everyone affected by yesterday's tragedy. Thank you for continuing to keep them in your thoughts and prayers, and thank you all for the incredible support you've shown me and my family.”

This is a developing story. More to follow.