MONTCLAIR (CBS) — A robbery at a jewelry store in Montclair Plaza forced a mall to be put on lockdown Thursday night.

The robbery reportedly happened at about 8 p.m. at a jewelry store inside the mall by several armed men.

Four men entered the mall, armed with rifles and handguns, and conducted what is known as a “smash and grab” at the store, police said.

At least a dozen patrol cars, ranging from Montclair, Upland, Chino, and the CHP, responded to the scene.

There was some concern that suspects might still be in the mall, which prompted authorities to place it on lockdown, so a search could be conducted.

“When this initially happened, there were areas of the mall that we did have to close off and orderly evacuated people out of certain corridors we had set up for then. So we could safely evacuate them, at the same time, keeping an eye out for suspects that may be in there,” said Lt. Jason Reed of the Montclair Police Department.

He said there was concern that the suspects might try to blend in with shoppers and leave with them.

“Officers on seen are apprised of the suspects’ descriptions at this time, so they are scanning people. Actually there have been a couple people detained at this time, that are exiting but we’re either ruling them out and sending them on their way,” Reed said.

Many shoppers were stranded inside the mall during the lockdown, but were released one at a time, according to a shopper, who did not want to be identified.

There were no immediate reports of any injuries.