NEW ORLEANS – Four people were shot on a very crowded Bourbon Street as revelers partied Saturday night amid the countdown to Mardi Gras, sending people running, police and bystanders said.

Two males and two females were wounded just before 9:30 p.m. local time, New Orleans police spokesman Frank B. Robertson told The Associated Press. He said one male was in critical condition and was undergoing surgery, while the other three were in stable condition. He did not release their ages.

Robertson said detectives were working vigorously to identify a suspect and determine a motive. He did not have any other details.

“They’re just piecing together what happened,” he added.

The streets were crawling with bar-hopping throngs taking in the last weekend before Fat Tuesday, the enormous party that engulfs New Orleans each year with parades, gaudy floats and costumed merrymakers tossing trinkets and beads to the crowds.

The iconic French Quarter street is home to strip clubs, watering holes and second-floor balconies lined by people who throw beads to revelers below each Mardi Gras season. The street often gets so jam-packed that officers have to control the crowds on horseback.

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 towards 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, yellow crime scene taped roped off an area of the street littered with trash, plastic bottles and other debris as police stood about. WWL-TV reported that police had obtained surveillance video from one of the establishments as part of the investigation.

“We don’t know what happened but they shut down the entire block for an hour,” Peter Manabani, an employee at the Rat’s Hole bar, told AP as loud music thumped in the background. He said the block reopened shortly before midnight and his establishment was crowded going into the wee hours.

Parades rolled all day Saturday but none on Bourbon Street because the streets are too narrow. One of the biggest Mardi Gras parades, the Krewe of Endymion, rolled down Canal Street and just skirted Bourbon Street a few hours before the shooting. Typically, once the parades end, partygoers head to the French Quarter.