Paradegoers recount panic during shooting after Chiefs Super Bowl rally: 'Everybody started running'

A celebration turned into chaos on Wednesday in Kansas City, Missouri, after gunfire erupted following the parade and rally for the Chiefs' Super Bowl win.

One person was killed and at least 21 people injured by gunfire in the shooting, according to Kansas City police.

The incident occurred west of Union Station, outside near the garage, as Chiefs fans were leaving, according to police. Three people have been detained for investigation in the shooting, police said.

About 1 million paradegoers were expected at Wednesday's celebration. Several recounted the fear and panic that pervaded following the shooting.

Julie Mobley told ABC News that the Chiefs players had just finished speaking when she thought she heard fireworks. Then her daughter pulled her to the ground.

"It was very scary," said Mobley, who took off work to attend the parade with her daughter. "To have something like this was absolutely horrible."

Mary Althiser, who was at the parade with Mobley, also ducked to the ground.

"At first it didn't seem like anything but then you saw this huge rush of crowd trying to jump in to where you were," Althiser told ABC News.

Paradegoer Arnold Sauther said when the rally ended the Chiefs went into Union Station, and fans followed the players to get autographs.

"Then, all of a sudden they all started running out, and you see all these policemen come running in there -- and you knew something happened in the station," Sauther told Kansas City ABC affiliate KMBC.

"People started crashing forward, everybody started running, there was screaming," one woman visiting from New Hampshire told KMBC. "We didn't know what was happening, but in this day and age when people run, you run."

She said they sought shelter near an elevator and "prayed."

"There was yelling and we didn't know if it was safe to leave, so we tried to block the doors. We heard the elevator start to move so we opened the doors and ran out -- there were officers there," she said. "I've never been so glad to see an officer in my life."

Witness Jennifer Wilbers told KMBC she heard gunshots and started running.

"We look over and there's a guy next to us on the ground," she told the station.

Kansas City Police Chief Stacey Graves called the shooting a "tragedy." Authorities are still working to determine the number of victims in the incident, she said.

A motive remains under investigation, the chief said.

Gene Hamilton told ABC News he is worried about how gun violence will impact young paradegoers.

"I look at the children. They have to grow up with this -- very disturbing," Hamilton said. "This is a celebration."

Paradegoer Zachary Dial told ABC News he and his family were stranded and unable to get to their car due to a lockdown following the shooting.

"I just wanted to make sure that my woman was good, my niece was good and that we could get home safely. I feel sorry for the ones that didn't," Dial said.

Kansas City Mayor Quinton Lucas, who was at the parade with his wife and mother, was also among those who ran for safety.

"We never would have thought that we, along with Chiefs players, along with fans, hundreds of thousands of people, would be forced to run to our safety today," he said during a press briefing on Wednesday.

He said he is "heartbroken" for the victims and their families.

"This is a day that a lot of people look forward to, something they remember for a lifetime," he said. "And what they shouldn't have to remember is the threat of gun violence marring a day like this, injuring them and their families."

ABC News' Emily Shapiro and Leah Sarnoff contributed to this report.