(NY Daily News)  A 16-year-old girl was shot dead while babysitting her little cousin inside their Brooklyn apartment Tuesday — and now cops are looking for her boyfriend, police sources said.

Shemel Mercurius moved four years ago from her native Guyana to the East Flatbush apartment she shared with her aunt and cousin, relatives said.

The teen was with her boyfriend, watching over 3-year-old Josia, when gunfire rang out and she was hit several times just before 6 p.m. in the sixth-floor pad in the Flatbush Gardens on Brooklyn Ave. near Foster Ave., according to police sources.

Rescuers found Shemel semi-conscious and rushed her to Kings County Hospital, but she couldn’t be saved.

Josia was unharmed in the bloodshed, cops said.

Shemel’s parents still live in Guyana, said her devastated grandmother, Joan Mercurius, 70.

“I haven’t been able to reach her parents,” she said. “We brought her here for a better life. We hoped she could go to college.”

Mercurius said Shemel was looking forward to finishing up the school year at Edward R. Murrow High School and taking a summer job.

“She was so cute, and she grew up so fast,” she said. “This is so terrible.”

About two weeks ago, Shemel’s grandfather took away her phone “because of some boy,” her grandmother said, but she wouldn’t elaborate.

“Oh my God! She was a wonderful child,” the distraught relative said. “She was never in any trouble.”

Bobby Blake, 39, who lives in the building, said he was getting his hair done when he heard the gun blasts and then someone running down the stairs.

“It was like crashes, but muffled,” Blake said. “After the loud bangs he was jetting down the steps, and my dog ran to the door.”

When he opened the door minutes later, the building was swarming with cops and security guards, he said.

Blake said he was stunned that the gunplay led to Shemel’s death.

“She was a sweet, loving little kid,” he said. “She’s not the type to be in any problems. She wasn’t raised in the street. She was a very decent person.”

Cops were hunting for the teen’s boyfriend and had not yet found or identified him early Wednesday, sources said.

The shooting came on the eve of Gun Violence Awareness Month, as politicians and advocates called for stronger gun control measures and more funding for neighborhood anti-violence groups.

“God willing, at some point, we can stop all this. Fifteen, it’s obscene,” said City Councilman Jumaane Williams (D-Brooklyn), referring to Shemel’s untimely final age. “It should be viewed as obscene each and every time that it happens.”

At 9 p.m. Tuesday, just hours after Shemel’s death, a 19-year-old man was shot in the back and leg on Rockaway Ave. near Livonia Ave. in Brownsville, cops said.

He was taken to Brookdale Hospital with injuries that were not considered life-threatening.

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