WACO, Texas » Many streets were nearly deserted in Waco, apart from law enforcement officials keeping watch, as night fell following a shootout between rival motorcycle gangs at a restaurant that left nine bikers dead and raised the specter of further violence.

Authorities increased security to quell other possible attempts at criminal activity in the Central Texas town following the melee Sunday that also left 18 bikers wounded, Waco police Sgt. W. Patrick Swanton said.

The violence erupted shortly after noon at a busy shopping center along Interstate 35 after members of at least five rival gangs gathered at Twin Peaks restaurant for a meeting, Swanson said. Preliminary findings indicate a dispute broke out in a bathroom, escalated to include knives and firearms and eventually spilled into the restaurant parking lot, according to police.

"I was amazed that we didn’t have innocent civilians killed or injured," Swanson said.

The interior of the restaurant was littered with bullet casings, knives, a club, bodies and pools of blood, he said. Authorities were expected to work throughout the night to process the evidence at the scene about an hour and a half south of Dallas. About 150-200 bikers were inside during the shootout, and at least 100 were detained, authorities said. It wasn’t immediately clear how many were arrested.

Parts of downtown were on lockdown, and officials could be seen stopping and questioning motorcycle riders. Agents from the FBI and federal Bureau of Alcohol, Tobacco, Firearms and Explosives were assisting local and state authorities in the investigation.

"I am feeling a lot of anxiety," said Darhonda McFarland, assistant manager at Denny’s at the Flying J Travel Center. McFarland told the Waco Tribune about 30 bikers clad in black walked into the restaurant shortly after the shooting.

They sat down but then abruptly got up and left, she said. About five minutes later, a SWAT team arrived, searched the restaurant and questioned people in the parking lot.

"I have never personally been caught up in anything quite like this from such a personal point of view. It was too close for me," she told the newspaper.

Police and the operators of Twin Peaks were aware of the meeting in advance, Swanton said, and at least 12 Waco officers in addition to state troopers were outside the restaurant, part of a national chain that features scantily clad waitresses, when the fight began.

Officers shot armed bikers, Swanton said, adding that the actions of law enforcement prevented further deaths. It wasn’t immediately clear whether any of the nine dead were killed by police officers.

A statement sent Sunday night on behalf of Jay Patel, operating partner for the Waco franchise, said, "Our management team has had ongoing and positive communications with the police," and added that the restaurant was cooperating with the investigation.

But Swanton described the management as uncooperative with authorities in addressing concerns about the gangs and called Patel’s statement a "fabrication."

Rick Van Warner, a spokesman for the Dallas-based corporate franchisor, said the company is reviewing the circumstances surrounding the shooting and is "seriously considering revoking" the Waco location’s franchise agreement.

Van Warner said he couldn’t address what the franchise owners "did or didn’t do leading up to this," but added that the company is "very upset that clearly our standards of safety and security were not upheld in this particular case," he said.

McLennan County Sheriff Parnell McNamara, whose office is involved in the investigation, said all nine who were killed were members of the Bandidos or Cossacks gangs.

In a 2014 gang threat assessment, the Texas Department of Public Safety classified the Bandidos as a "Tier 2" threat, the second highest. Other groups in that tier included the Bloods, Crips and Aryan Brotherhood of Texas.

The Bandidos, formed in the 1960s, are involved in trafficking cocaine, marijuana and methamphetamines, according to the U.S. Department of Justice.

The Texas assessment doesn’t mention the Cossacks.

There’s at least one documented instance of violence between the two groups. In November 2013, a 46-year-old from Abilene who police say was the leader of a West Texas Bandidos chapter was charged in the stabbings of two members of the Cossacks club.

Associated Press videographer John L. Mone contributed to this report.