It happened around 6am at the Bronco Nite Club on Veterans Memorial near West Road in northwest Harris County.
Dozens of club patrons witnessed the shooting.
"The guy died in the parking lot because the security guard shot him," witness Brenda Romero said. "He shot him because he was drunk and he got into a confrontation with the security guard. The security guard came back and shot; that's it."
Witnesses said multiple shots were fired.
"I almost got shot," witness Lina Deleon said. "I had to run to the back."
According to the Harris County Sheriff's Office, the security guard was in the process of escorting several people out of the club at closing time when a fight started.
Detectives said the guard shot all four victims when they all assaulted him at once. One man died at the scene. Three others were taken to area hospitals. Officials said one had serious injuries and the other two were minor.
"The security guard: he has been assaulted; he has physical injuries, trauma injuries, not a gunshot wound," HCSO Sgt. Ben Beall said.
Romero told us she comes to the club often but has never witnessed things get this out of control. She said the deceased victim -- a man who appeared to be in his 20s -- was shot in the chest.
She tried to help him, but he died in her arms.
"I really don't know him," Romero said. "I was just trying to tell him to stay up with me to help him out."
Investigators spent the morning questioning club patrons. They are now looking into whether the club was able to sell alcohol.
According to investigators, the area is no stranger to problems. Officials say they have received 12 calls for service in the last two months at the strip center where Bronco is located. The owner of the club reportedly locked up the bar and left the scene after the shooting happened.
Detectives said they will complete their investigation at the scene and send evidence and witness statements to the district attorney's office, where it will be decided whether the security guard will be charged.