“This is very disappointing for us. It’s heartbreaking.”

The police chief, Richard Smith, said that officers were called to the bar, the 9ine Ultra Lounge, near Noland Road and U.S. Highway 40, at about 11:30 p.m. local time. The suspect, identified as Jahron Swift, 29, of Kansas City, had opened fire outside the club as people waited to enter, Chief Smith said.

The woman killed was identified as Raeven A. Parks, 25, also of Kansas City. It was not clear whether it was a targeted attack. The police said that only the suspect and the security guard, whose name was not released, had fired during the exchange.

“It appears that he saved lives,” Chief Smith said of the guard.

He added that responding officers encountered a chaotic situation, with hundreds of people fleeing in cars and on foot. Multiple firearms were recovered at the scene, he said. The police did not specify the weapons’ models.

“It was a very intense scene, to say the least,” he said.

At least 15 people turned up at local hospitals saying that they had been injured in the attack, Chief Smith said. The Police Department had previously said on Twitter that three of those people were in critical condition.

Jean Peters Baker, the Jackson County prosecutor, said in a telephone interview on Monday that it appeared the gunman had acted alone.