(CNN) — Three children have died after they were found unconscious on the shores of Coney Island in Brooklyn early Monday morning. The New York Police Department said authorities are questioning a woman believed to be his mother.

The 30-year-old woman, who is believed to be the mother of a 7-year-old boy and 4-year-old and 3½-year-old girls, the department’s chief, Kenneth Corey, said at a news conference Monday morning.

He was not in custody at the time and the investigation was “very active,” he said. As of Monday afternoon, New York police confirmed to CNN that the woman remained at a local hospital. No charges have been filed against her yet.

There was no indication of prior neglect or abuse, Cory said, citing preliminary information.

“We don’t know exactly what happened here,” he said, stressing that the information he provided was preliminary.

Police received a 911 call around 1:40 a.m. from a concerned person saying a family member may have harmed their three children, Corey told reporters. Agents went to the apartment but there was no answer.

A man who identified himself as the father of one of the children met with officers at the building and shared the caller’s concerns. According to Corey, he told police he believed the woman and children were on the Coney Island boardwalk.

Agents began searching for the woman and children, searching the boardwalk, the beach, surrounding streets and the local hospital.

Time Trial Search

According to Corey, the search lasted about 90 minutes before another 911 call sent officers to Brighton 6th Street and the Regalman Boardwalk in nearby Brighton Beach, where they found the woman and her family members. A police spokesman told CNN that the call referred to a woman who had been shot.

Corey said the female officers were “drenched” but it was unclear whether she was in the rain or standing in the coastal waters.

The children were not with her, and a search with ground, air and port units continued until 4:42 a.m., when agents located the children along the shoreline of West 35th Street in Coney Island, three kilometers from where the woman was found.

Officers immediately began CPR on the boys, who were taken to Coney Island Hospital and pronounced dead, Corey said.

CNN’s Mark Morales and Liam Reilly contributed to this report.