Two young boys were discovered fatally stabbed on Thursday inside an apartment in a luxury building on the Upper West Side of Manhattan by their mother, who came home from work to find a horrific scene.

The children’s nanny, who was found with a self-inflicted stab wound, was arrested after the stabbings inside the apartment at 57 West 75th Street, the police said.

One neighbor, who declined to give his name, reported hearing screams around 5:30 p.m., around the time that the children’s mother arrived home from work to find her children, boys ages 6 and 2, stabbed and in a bathtub.

The police declined to provide details about those stabbed. The police said the boys were pronounced dead at St. Luke’s Hospital, where the nanny was in extremely critical condition.

“It’s a chaotic scene,” a fire official said.

Neighbors watched nervously as several of those injured in the stabbing were taken out on stretchers and loaded into ambulances. The entire block, from Central Park West to Columbus Avenue, was shut down by the authorities.

The building, the La Rochelle, a block west of Central Park, is an 11-story prewar complex with grand columns at the entrance.