Jewelry stores are on alert after thieves were caught on camera smashing glass with a sledgehammer and taking jewelry across the city.

Police are investigating one of those robberies in Fordham Heights where the store Grand Jewelers was the site of a smash-and-grab.

Police are investigating at least 18 across the city that appear to be connected.

The incident happened on Friday, and the store's gate played a role in preventing the suspects from taking more jewelry.

Surveillance video shows two men that store owner Marjory Amoros says she thinks acted as lookouts before someone with what looks like a sledgehammer comes and breaks the window.

"In the eight years that I've been here, no, It has never happened. It was the first time, we were lucky in the riots," Amoros says. "When that happened, I ran as quickly as I could to put down the gate from the inside. Once we did that, we called 911."

The store owner says the men ran off with $100,000 worth of jewelry that was uninsured, but they were able to recover some of the dropped jewelry.

"Some people were really nice and picked up the jewelry from outside, threw back through the gate back to us. There's good people here," Amoros says.

Police have also responded to other recent smash-and-grabs in the Bronx over the past month.

News 12 covered one in early April on Westchester Avenue. Another one occurred on White Plains Road on the Grand Concourse Sunday.

"I do not feel comfortable in the area after the robbery because before I would be able to walk around the street with my jewelry on," said MNP Jewelry store employee Yailin Rivera.

She was working Sunday when a group of men walked by, broke the glass to the store and grabbed as much jewelry as they could.

"I don't know how much to be exact, but I don't think they took a lot because I was able to put the gate when I heard the boom," Rivera said.

Police say sledgehammers were also used in those incidents.

Police, so far, have not linked the Grand Concourse heist to the one on White Plains Road, but they say they believe the people who robbed the White Plains Road location targeted at least 17 others all across the city.

It's not clear what kind of vehicle they used to get away but some of the police reports mention a black BMW.

Authorities are asking anyone with any information about the robberies to call Crime Stoppers at 1-800-577-TIPS.