Updated 04/30/14 – 12 p.m.

CHICAGO (CBS) — Police were warning some lakefront residents to be on alert, after someone shot out windows at a North Side high-rise at least three times in the past 10 days.

CBS 2’s Susanna Song reports someone has been shooting some type of projectile at windows at the Harbor Point condo tower at 155 N. Harbor Dr. – twice late at night, and once just before dawn. At least five windows have been shattered.

The latest incident was Monday night, around 11:30 p.m. Windows also were shot out Sunday night and just before dawn on April 20.

Detectives would not say if a gun was used, or if it was some other type of projectile such as a slingshot.

Wednesday morning, several windows were still boarded up on the concourse level, near the building’s gym and swimming pool.

Police warned residents of the building to be on the lookout.

Residents said they were stunned by the incidents, and concerned children could have been injured.

“It’s not a game. It’s not. It’s not funny. It’s not funny at all,” said Tanya Thomas. “We swim in the pool. How are you going to stop it? What’s the building going to do? Put a cement block around the building?”

Thomas said several children and elderly people live in the building and use the pool.

“I’m training for a triathlon, so I use the pool,” she said.

Building managers did not return calls seeking comment on the incidents.