Police are investigating a string of fights in malls across the country on one of the busiest shopping days of the year. There were reports of disturbances in more than a dozen cities Monday, from Elizabeth, New Jersey, to Fort Worth, Texas. Some police departments said they were responding to reports of shootings.

Police believe that, in some situations, postings on social media drew attention to the fights, reports CBS News correspondent Jericka Duncan. But while they all happened within a few hours of each other, it’s still unclear whether they occurred by chance or were planned.

Dozens of police officers rushed in to respond to a fight at the Fox Valley Mall outside of Chicago. Confused and panicked shoppers scrambled for building exits. Police say nearly 1,000 teens gathered at the mall before the brawls started at around 6:30 p.m. The mall closed for over an hour.

At a shopping center in Elizabeth, New Jersey, officers armed with long rifles and riot shields searched the food court after someone shouted “gun” after a chair slammed. Hundreds ran for the exits, resulting in at least eight injuries. Video shows corridors choked with shoppers trying to get out.

In Fort Worth, Texas, officers responded to reports of an active shooter, although it turned out there was no gunman.

“Anytime that we’re hearing a mall shooting, and it’s the day after Christmas, you have tons of people holiday shopping, of course the response is going to be just like that. We’re going to get in here as fast we can,” Fort Worth police spokeswoman Tamara Valle said.

Police are still unsure about why nearly a dozen brawls happened around the country. In at least one situation, authorities say social media post may have played a role.

“Running, screaming. I seen a girl get trampled over. It was scary, it was really scary for real,” one witness at Beachwood Place Mall in the Cleveland suburb of Beachwood, Ohio said. The mall was placed on lockdown and officers used pepper spray to disperse a large crowd after a fight.