Three people were killed and seven others were injured, several of them critically, after a shooting at an In-N-Out Burger restaurant in the US city of Twin Falls, Idaho, on Saturday, authorities said.

Police responding to the incident found the suspected gunman dead near the restaurant, although officials did not immediately confirm whether the suspect was included in the death toll.

Twin Falls Police Chief Matthew Hicks said investigators were still working to establish the shooter’s identity and motive.

“We believe the threat to the community is over,” Hicks told reporters, describing the scene as “very chaotic.”

Authorities have withheld the identities of the victims while family members are being notified.

Several of the injured remain in critical condition, according to city spokesperson Josh Palmer.

The shooting occurred at around 2pm local time at an In-N-Out Burger restaurant in a busy shopping plaza, where hundreds of people were in the area.

Investigators continued interviewing witnesses as they pieced together the sequence of events.

Eyewitness Lane Koehn said he was waiting at a nearby traffic light when he saw a person carrying an AR-style rifle emerge from the restaurant’s drive-thru. He said another man armed with a handgun opened fire on the suspected shooter.

Koehn later helped an In-N-Out employee who had dragged a wounded female colleague, who appeared to have been shot in the chest, across the parking lot while waiting for paramedics to arrive.

Another witness, Haley Dodaro, said she and her mother were in the drive-thru when they saw people fleeing the restaurant in panic.

Initially believing there had been a fire, they soon learned from a traffic marshal that an active shooter was on the scene.

“People were running out crying and screaming. It was very scary,” she said.

Customer Nayeli Rodriguez said she was inside the restaurant with her daughters when gunfire erupted from the kitchen area. An employee warned customers to get down before they fled the building.

Video recorded by a passing motorist appeared to show a man dressed in black carrying a long rifle near a white vehicle before opening the trunk, prompting the driver filming the scene to leave out of fear that additional weapons were being retrieved.

Multiple victims were taken to St. Luke’s Magic Valley Medical Centre for treatment.

The hospital said it was working closely with law enforcement and emergency responders.

The restaurant had opened only nine days earlier, on July 24, as part of In-N-Out Burger’s expansion into Idaho.

Twin Falls, home to about 56,000 people, is located roughly 205km southeast of Boise.