An attacker who “brutally assaulted” a woman later found just outside her apartment remained on the loose Monday night but has likely left the area, Long Beach police said.

“This is an isolated incident, and we don’t believe the offender is still in Long Beach,” Police Commissioner Michael Tangney said Monday. “We believe the victim was targeted.”

Officers responding to a 911 call late Sunday at an apartment building on New York Avenue in Long Beach found the victim with serious injuries after the beating, police said.

The unidentified woman, 54, sustained “blunt force trauma to her head,” Long Beach police said in a statement, and was taken to a hospital in serious condition. Information on the attacker’s relationship to the victim or any other information was not available.

Police said the victim “underwent surgery” and her condition had not changed Monday.

No arrests have made in connection with the attack, although investigators are pursuing leads, Tangney said.

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The assault took place in the vestibule of the small, two-story apartment building, police said.

Resident Laura Stone, 69, said she was home at the time.

“I heard four screams,” Stone said. “Then I hear my neighbor screaming. . . . I came out and I saw [the victim] lying on the floor.”

Mike Cloutsis, 48, said he was home watching football when he heard the victim collapse to the floor just outside his unit.

“I opened my door and saw her lying face-up on the floor,” Cloutsis said. “I said to her, ‘Hello! Hello! Can you hear me? You’re going to be OK!’ But nothing. She just had a blank stare.”

Cloutsis said he alerted the victim’s best friend, who also lives at the complex, and they called police.

With John Valenti