Ms Brown, 21, was rushed to hospital on Saturday after being found unconscious in the bath at her home in Atlanta. Photo: Reuters

Ms Brown, 21, was rushed to hospital on Saturday after being found unconscious in the bath at her home in Atlanta.

Her mother, a global star, was found dead in February 2012, aged 48, in a bath in a hotel in Los Angeles.

The hospital has not commented on her condition but her family said they were by her bedside.

In a statement, Ms Brown's family said: "Bobbi Kristina is fighting for her life and is surrounded by immediate family."

"We are asking you to honour our request for privacy during this difficult time."

On Monday, police said they were called to her home in suburban Atlanta on Saturday in response to a "drowning".

A police official told a local broadcaster officials had not found any drugs or prescription medications in the home.

A spokeswoman for North Fulton Hospital declined to comment on Ms Brown's condition, citing medical privacy laws.

An unidentified source close to the family told CNN Ms Brown was in a medically-induced coma and breathing with the aid of ventilator.

Whitney Houston was seen as the golden girl of the music industry in the 1980s and 90s, becoming one of the world's best-selling artists and the most successful soul singer of all time.

But the hits stopped in the mid-1990s after she began to abuse cocaine, marijuana and prescription drugs.

A post-mortem examination later concluded she died of accidental drowning due to the effects of cocaine use and heart disease.

Bobbi Kristina was born after the singer's tumultuous 1992 marriage to hip-hop singer Bobby Brown.