Hundreds of people were at 9ine Ultra Lounge -- owned by former Chiefs 5th-round draft pick Alphonso Hodge -- when a 29-year-old gunman opened fire ... killing a 25-year-old woman.

15 others were injured before a security guard shot and killed the alleged shooter, Jahron Swift ... police said at a news conference on Monday.

“Last night was a night a lot of people were dreaming of for 50 years,” Kansas City mayor Quinton Lucas said.

“While we won't necessarily say that folks aren't still happy, but this a very disappointing for us.”

We're told no Chiefs players were present at the bar at the time of the shooting.

Kansas City police chief Richard Smith said Hodge was at the club at the time of the shooting and is cooperating with law enforcement.

Hodge spent parts of two seasons with the Chiefs, although he did not appear in any regular-season games.

He also spent time with the New York Jets.

Hodge's club issued a statement on the shooting, saying ... "The 9ine ultra lounge family and organization is deeply saddened by the unsavory tragic act of one individual last night."

"Our deepest sympathies go out to the injured, the deceased and their loved ones. This shameless and senseless act of violence claimed the life of one of our patrons and injured many others and quite frankly, we have little in the way of answers."

As for the shooter, police said they found multiple firearms in his possession.