Nicholas Latimer of Alfred A. Knopf confirmed her condition hours after celebrity columnist and friend Liz Smith published what appeared to be a memorial for the writer.
Smith told The Associated Press that she had spoken to Ephron's son Jacob on Tuesday morning and was told that Ephron was dying. She said when she heard that funeral plans had been arranged, she published the column on the website Women on the Web.
"I was confused because I was told to come to the funeral on Thursday," Smith said. "It's bad enough."
Latimer did not provide any additional information on Ephron's condition.
Ephron, 71, is best known for writing books like "Heartburn" and "Crazy Salad" and for the movies "When Harry Met Sally," "Sleepless in Seattle" and most recently "Julie & Julia."
Ephron, who has been a director, screenwriter and producer, is considered one of most influential women in Hollywood and one of the literary world's key authors.
"Heartburn," starring Meryl Streep and Jack Nicholson, chronicled her own dissolving marriage with journalist Carl Bernstein and was based on the novel of the same name.
Ephron has two sons, Jacob and Max Bernstein.