Whitney Houston was underwater and apparently unconscious when she was pulled from a Beverly Hills hotel bathtub, and she had prescription drugs in her room, authorities said on Monday.

The pop star's family made arrangements to fly her body home to New Jersey for a funeral at the end of the week.

Authorities had said there were no indications of foul play and no obvious signs of trauma on Houston's body but that it could be weeks before the coroner's office completes toxicology tests to establish the cause of death. The 48-year-old singer had struggled for years with cocaine, marijuana and pills, and her behaviour had become erratic.

However, officials have now told her family she may have died before she became fully submerged in the water following a drink and drugs binge.

Houston was found underwater Saturday at the Beverly Hilton Hotel by a member of her staff about 3.30pm, hours before she was supposed to appear at a pre-Grammy Awards gala, police Lt Mark Rosen said. She was pulled from the tub by members of her staff, and hotel security was promptly notified, Rosen said. She was pronounced dead about a half-hour later.

It is believed only a small amount of water was found in her lungs, which medics claim was not enough for her to have drowned.

Investigators are also working on the theory she suffered a heart attack caused by an adverse reaction to her medication.

Los Angeles police - who obtained a search warrant for the fourth-floor suite at the Beverly Hilton Hotel - are said to have found six prescription pill bottles, Xanax, Lorazepam, Ibuprofen, Midol, Amoxicillin and Valium.

Now detectives investigating her tragic death will question up to nine doctors they believe could have supplied her with the lethal cocktail of prescription drugs.

They want to know how the mother-of-one - who had a history of drug and alcohol abuse - was able to get hold of such a vast quantity of substances

A source said: "Investigators will speak to her doctors. Even though it appears to be prescription pills that may have killed her as opposed to illegal street drugs, the authorities need to be satisfied she had these drugs in her possession legally.

"They need to determine that no one is criminally negligent. There could still be charges in this case."

"As of right now, it's not a criminal investigation," Rosen said, refusing to release further details. "We have concluded our portion of the investigation at the hotel."

Los Angeles coroner's assistant chief Ed Winter said there were bottles of prescription medicine in the room. He would not give details except to say: "There weren't a lot of prescription bottles. You probably have just as many prescription bottles in your medicine cabinet."

The coroner's office released the body to the family late Monday morning. Two people who spoke with Houston's family said the singer would be taken to New Jersey. The two, who spoke on condition of anonymity because they weren't authorised to speak for the family, said Houston's family raised the possibility of a wake Thursday and a funeral Friday at Newark's Prudential Centre, an arena that can seat about 18,000.

Houston was born in Newark and raised in nearby East Orange. She began singing as a child at Newark's New Hope Baptist Church, where her mother, Grammy-winning gospel singer Cissy Houston, led the music program for many years.

The White House said President Barack Obama's thoughts and prayers were with Houston's family, especially her daughter.

Houston's death tinged the Grammy ceremonies with sadness. It also probably boosted viewership, which was 50 per cent higher than last year, with nearly 40 million viewers tuning in.

A sensation from her first album, Houston was one of the world's best-selling artists from the mid-1980s to the late 1990s, turning out such hits as I Wanna Dance With Somebody, How Will I Know, The Greatest Love of All and I Will Always Love You. But as she struggled with drugs, her majestic voice became raspy, and she couldn't hit the high notes.

Mourners left flowers, balloons and candles at the wrought-iron fence around the tall brick Newark church where she got her start. It sits near an abandoned housing project and the train line leading to New York City.

"She was an inspiration to everybody," said Gregory Hanks, an actor who grew up in the neighbourhood and who dropped off a bouquet. He saw Houston perform in New Jersey years ago.

"I grew up listening to her as a little boy, and to hear her sing, you knew she was special," he said.