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(NBC CHICAGO) -- After a harrowing two hours, the Chicago Police Marine unit has rescued a dog trapped on a frozen Lake Michigan harbor.

The dog was spotted on the ice at Jackson Park Harbor around 9 a.m. on the 6700 block of South Lake Shore Drive. A Marine Unit diver was seen on the ice at 10 a.m. trying to coax the dog back in, but the pup didn't surrender quickly.

Helicopter footage showed the dog jog back toward shore several times only to head farther onto the ice. The back-and-forth went on for another agonizing half hour before crews surrounded the dog near shore.

The dog laid down on the ice as police and Marine units approached while pedestrians watched nearby. Rescuers tranquilized the dog before they put a collar around him, police said.

The dog is now in the custody of the animal care unit. Police said the dog did not have a collar on at the time of the rescue but could have a chip.

Tuesday morning was the coldest in Chicago in two years with wind chills hovering around -10 degrees.

The dog became trapped just as firefighters responded to a 3-11 alarm high-rise fire blocks away on the 6700 block of South Shore Drive. Three people were taken to local hospitals in critical condition. Firefighters extinguished the blaze by 9:25 a.m. and began an investigation into the cause.