Baltimore Police announced Wednesday that officers have arrested at least nine adolescents in a series of carjackings targeting Uber and Lyft drivers—and in some cases customers—in Baltimore City and Baltimore County.

“It is organized,” Deputy Baltimore Police Commissioner Richard Worley said. “It is usually about five to six suspects. They rob a rideshare driver, and they take their app and start answering calls.”

Worley said they have closed five cases including three in the city and two in the county.

Officers arrested five people in connection with two carjackings in Baltimore City on Tuesday alone.

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One of those carjackings happened around 3:30 p.m. on Chrysler Avenue in Northwest Baltimore on Tuesday.

A neighborhood resident told WJZ that a postal worker witnessed the incident and rushed to her door to ask that she call 911.

Baltimore Mayor Brandon Scott said at a news conference that the young carjackers are often repeat offenders.

“Our detectives are out here busting their butts, making these arrests, only to have to go after the same crew several months later,” Scott told reporters.

Worley said a special group of officers is working with federal partners to crack down on the crimes involving rideshares.

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“We have a team of people who look at every single robbery that comes out,” he said. “We put it out on our messaging—our Evertel messaging—so within minutes, we know what car has been taken, what route it has taken. What they’re doing is they are moving around the city. It’s not just confined to a small area.”

Worley said ride-hailing apps are still safe to use and only a small percentage have been targeted.

“There are so many rideshares in the city,” he said. “This is a small number of them, but they are very violent when they do do it, when they do take over the car. We don’t want any of our citizens to become victims, but we also don’t want them to adjust their everyday life because there are some men and women out there who are creating havoc.”

There have also been cases in other cities, including a Lyft driver who fought off an armed attacker in Washington, D.C.

In New York, prosecutors released chilling video of a rideshare driver’s carjacking and said they had arrested a gang behind a series of violent crimes.

In Prince George’s County, police said two 14-year-olds used a replica handgun to carjack a driver over the weekend.