Updated at 6:35 a.m. ET: Two men and two women were shot in New Orleans' Bourbon Street after gunfire broke out while crowds gathered in the countdown to annual Mardi Gras festivities, police said on Sunday morning. 

Three of the victims were listed in stable condition while a male victim underwent surgery and was listed in critical condition, New Orleans Police spokesman Frank Robertson said.  

The shooting happened at around 9:30 p.m. (10:30 p.m. ET) after one of the victims got into an argument with two men, Robertson said. 

The two men left but soon returned, according to police.  One then shot one of the victims in the abdomen, upper thigh and pelvic area, and fled the scene, Robertson said.  

Police released video filmed by a bystander on a private camera that showed a crowded and chaotic street scene.

According to the police, the footage shows the two men arguing with the first victim and leaving the scene.  They soon return and start shooting the first victim. 

In addition to the first victim, one woman was shot in the buttocks and a second in the chin and right foot. As second male victim was shot in the toe, police said. 

The Associated Press earlier reported the following: 

Patrick Clay, 21, an LSU student, told The Times-Picayune he was standing on the corner of Bourbon Street when suddenly he saw a crowd running and people screaming that there was a shooting. 

"Everyone immediately started running and the cops immediately started running toward where people were running from," Clay said. "I was with a group of about seven people and at that point we all just kind of grasped hands and made our way through the crowd as soon as possible."

Afterward, police moved in to investigate. Many revelers said they stayed hunkered down in bars and other establishments until police cleared them to move freely.

Crowds gather each year in New Orleans' French Quarter for celebrations that build to a climax on Fat Tuesday, which this year falls on February 12.