BUFFALO — Four people were shot to death early Saturday when gunfire erupted as a crowd of partygoers was leaving a popular restaurant in the city’s downtown business district, officials and others said.

Four more victims, all men, were wounded in the 2:30 a.m. shooting outside the City Grill on Main Street, said Michael DeGeorge, a spokesman for the Buffalo Police Department. The party, involving more than 100 people, was held to celebrate a wedding that took place last year, the authorities said. The groom was one of those killed, the police said.

“An occasion that should have been a joyous one, a happy one, turned to tragedy,” the mayor, Byron Brown, said at a news conference.

Within nine hours of the shooting, one of the worst in the city’s recent history, investigators were on the trail of someone they believed to have been involved, Mr. DeGeorge said. “There has been some progress made in the investigation,” he said.

The groom was not immediately identified. Reached by phone on Saturday, Ruby Martin, 45, identified two of the victims as her daughter, Tia McNeil, 25, and a cousin, Tiffany Wilhite, 32.

“I don’t know what happened,” Ms. Martin said. “Somebody was just shooting randomly. She got hit and her cousin got hit, and both of them died.”

The police commissioner, Daniel Derenda, said a fight in the restaurant had led to the closing of the bar, and patrons were being asked to leave.

Mr. DeGeorge said the shooting occurred as someone let loose a burst of gunshots while the party was breaking up. Calls to 911 streamed in afterward, he said.

Latoya Nuness, who was in the restaurant, said she and friends were leaving when they heard the shots and ran back inside.

“I’ve never been through anything so crazy,” she said.

Ms. Nuness and her friends went into the kitchen and hid from the carnage. “They were just shooting whoever they could shoot,” she said.

The bar at the City Grill, nestled within the shadow of the city’s tallest building, the HSBC tower, serves as a hub of post-game activity for crowds leaving Coca-Cola Field, the home of the Mets’ AAA affiliate, the Buffalo Bisons.

The commissioner pleaded during a news conference for more witnesses to come forward. “I can’t stress enough,” he said, “any information, we need to hear it, and we need to hear it now.”

They arrested the wrong man.

He's still being held on a parole violation while they continue to investigate.