Police said they fatally shot a man who entered a US supermarket with an AR-15-style rifle and "plenty of ammunition".
Omaha Police Chief Todd Schmaderer said officers searched for victims, including customers and workers at the Target store "because there were some people hiding in there".
No injured people were immediately found.
Dozens of officers are said to have responded, according to reports.
Schmaderer said evidence suggests the man fired multiple rounds before he was shot by officers, but it wasn't immediately known if he fired at anyone.
The chief said there were several 911 calls and officers were at the store within minutes.
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"The first arriving officers went into the building, confronted the suspect and shot him dead," Schmaderer said.
"He had an AR-15 rifle with him and plenty of ammunition."
“When you have a mass shooter in your city you want a massive response like this,” Schmaderer added.
Officer Chris Gordon, a police spokesperson, said the store in west Omaha was locked down at about noon on Tuesday, after reports of shots being fired.
Remus Smolksy told Fox5 Las Vegas he saw people running out of the store, including a woman and her two children, when an employee told him there was a shooter.
“I went in and I looked left down at the frozen area and I looked right all the way down to the other end of the store I could see and I couldn’t see anyone else in there.
"That’s when I heard something else that sounded like a shotgun,” he said.
Cathy Mahannah, a customer, said the scene inside the store was “sheer panic.”
