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New York City police are hoping to interview a nanny after two children were discovered stabbed to death in a luxury apartment on Thursday evening.

Yoselyn Ortega, 50, is in a critical condition with self-inflicted stab wounds to her neck, say police.

The children's mother, Marina Krim, returned to her Manhattan home to find the bodies of two-year-old Leo and six-year-old Lucia in the bath.

Officials say it is not clear how long the nanny had worked with the family.

Charges have not yet been filed.

The children's father, CNBC digital media executive Kevin Krim, was informed by police of the situation as he arrived at the airport on his way home from a business trip.

On a Friday conference call, chief executive Brian Roberts, of CNBC's parent company Comcast, expressed his condolences to the Krim family and said the company would do "everything we can to support the family in their awful time".

When Mrs Krim returned home with her three-year-old, Nessie, on Thursday afternoon the flat was dark and she thought the nanny had taken her other two children out, Police Commissioner Raymond Kelly said.

Mrs Krim went downstairs to ask the doorman of the building whether he had seen them leave, but he said no, Commissioner Kelly added.

Mrs Krim found her dead children when she returned to the flat. It is not known how many times the children had been stabbed.

According to police, Ms Ortega began stabbing herself as the mother entered the bathroom and began screaming when she saw the children in the bathtub.

"We initially thought it was, it had already been done, but now information is coming out that she did it as the mother entered the room," Commissioner Kelly said on Friday.

Rima Starr, a music therapist who lives on the same floor as the Krim family, heard screams coming from the flat at around 17:30 (21:30 GMT), the Associated Press reported.

"There was some kind of screaming about 'You slit her throat!'" Ms Starr said. "It was horrible."

After the police arrived, Ms Starr said Mrs Krim was in the building's lobby crying and screaming hysterically, and clutching her surviving child.

Another neighbour, Sandy Marcus, described the mother as "inconsolable, hysterical, frantic", the Wall Street Journal reported.

Mrs Krim lovingly chronicled her children's upbringing in a blog, Life with the Little Krim Kids, which has now been taken offline.

AP news agency says that in a February blog entry, Mrs Krim wrote about visiting their nanny's family in the Dominican Republic.

It is not clear if the person she refers to is the woman found wounded in the Manhattan apartment.

Mrs Ortega is said to have lived with her sister and niece.

Her building superintendent, Fernando Mercado, described her as a "very nice woman" who seemed to be "very stable", the Associated Press reported.