A 25-year-old woman was killed and 15 people were injured outside a Kansas City, Missouri, nightclub on Sunday night when a gunman let loose a barrage of shots before he was gunned down by a security guard, authorities said on Monday.

The shooting happened outside the 9ine Ultra Lounge, where several hundred people had gathered, many celebrating the Kansas City Chiefs' American Football Conference championship and a birth to the team's first Super Bowl in 50 years, said Kansas City Mayor Quinton Lucas.

"We're here today because something happened last night that marred what was an exciting night, a euphoric night for the people of Kansas City," Lucas said at a news conference Monday afternoon. "First of all, this city will never stand for this type of gun violence. We will continue to try to stop it before it starts and we'll make sure that with any investigation we're bringing folks to justice."

He conceded the shooting mirrors "a problem in Kansas City."

"We've said a few times that it is an epidemic of gun violence. We're losing too many lives. We have too many people shot each year," the mayor said.

Kansas City Police Chief Richard Smith said his department was already on high alert when the shooting broke out with extra police assigned to overtime shifts in anticipation of Sunday's NFL game and the spontaneous celebrations that broke out afterward across the city. The Chiefs clinched a spot in the Super Bowl for the first time since 1970.

He said police officers had checked the parking lot outside the 9ine Ultra Lounge in the southeastern part of the city less than a minute before the shooting started at 11:27 p.m.

"This club had come up previously. We knew it was an issue at some other points of time in the past," Smith said, noting that a drive-by shooting occurred outside the club last week. "Officers had done a check of the parking lot and were less than a minute out when we received our first call. So we had just been there."

When officers returned to the club, they encountered a chaotic scene.

"We had hundreds of people fleeing both in cars and on foot," Smith said.

The alleged gunman, Jahron Swift, 29, of Kansas City, apparently had gotten into a confrontation inside the club and once outside, began shooting people who were in a line waiting to get in, Smith said.

Smith identified the victim killed in the shooting as 25-year-old Raven Parks.

"The security guard is the one who engaged the suspect," said Smith, who did not release the name of the security guard.

He said the security guard heard the gunshots and went outside and confronted the gunman, fatally shooting him.

"It appears he saved lives," Smith said.

Smith said it remains unclear how many of the 15 injured people treated at hospitals suffered gunshot wounds.

No shots were fired by any of the 50 officers who responded to the scene.

He said most of the people injured in the incident were taken to area hospitals in private cars. Officials said three of those injured were initially in critical condition.

According to police, a line had formed to get into the bar when the suspect started shooting into the line of people.

Smith said the motive for the shooting remains under investigation.

He said police have found no evidence that the shooting was gang related.

Lucas said the city's Regulated Industries Division will begin investigating the club on Tuesday to determine if the business has become a public nuisance. Depending on the investigation, he said the club owner could face a fine or be forced to close.

The mayor said the club owner is cooperating with police.

"It's incredibly, incredibly frustrating," Lucas said of overall shootings in the city. "Last night, was a night people have been dreaming of for 50 years. We don't need to keep having disappointments like this."