OMAHA, Nebraska (Reuters) - A gunman opened fire inside a crowded shopping mall in Omaha, Nebraska, on Wednesday, killing eight people and then himself, police said.

Five people were wounded in the rampage at the Westroads Mall, two of them critically, according to hospital spokesmen. One man with a chest wound was in surgery.

Witnesses reported hearing as many as two dozen gunshots, telling a local television station the gunman shot one man in the head from a third-floor balcony and others at point-blank range as he moved through the mall.

"It was horrible, just horrible," one woman told KETV, saying she hid under a clothes rack when the shooting started.

Another witness at the mall, busy with pre-Christmas shoppers, said she heard someone shout: "It's a gunman, run!"

Most of the victims were shot inside one department store and the motive for the rampage was still being investigated, said Sgt. Teresa Negron of the Omaha Police Department.

"We do not believe that we have any other shooter," she told reporters. "The person we believe to be the shooter has died of a self-inflicted gunshot wound."

Mass shootings periodically shock the United States, where gun ownership is widespread and the right to bear arms is a hotly contested constitutional issue.

In mid-April, Virginia Tech university became the site of the deadliest shooting rampage in modern U.S. history when a student killed 32 people and then himself.

In October 2006, a milk truck driver tied up and shot 10 Amish schoolgirls in their classroom in Pennsylvania, killing five of them before turning the gun on himself.

According to KETV in Omaha, the county sheriff's office said it was given a note involving a 19-year-old man that could be interpreted as "suicidal." The note was found by someone after the shooting, although it was not clear where.

One woman told KETV she saw the gunman firing into the air inside the department store.

"I saw the guy in the children's department. He was tall, real tall," she said. "He had his hand straight up in the air, just shooting, not saying anything."

Jeffrey Peck, manager of a leather goods store, said mall workers ran up to tell him to close up his store.

"I told the customer to go into the back room and, as I was shutting the gate, I heard two gunshots ring out," he said.

Some of those shot were waiting in line to get Christmas presents wrapped at Von Maur, an upscale department store and one of the anchors of the mall.

Shoppers and store workers were trapped inside the mall, which has roughly 135 stores, and huddled behind locked doors or inside dressing rooms. Others streamed out of mall exits with their hands raised.

President George W. Bush gave an address in Omaha on Wednesday morning but had left the city hours before the incident.