Paramedics who arrived at Amy Winehouse's London home said she had been dead for "several hours at least."
She had spoken to her security guard, Andrew Morris, on Saturday morning at about 10 am, and told him she wanted to go to sleep.
When he went to wake her several hours later he found her dead.
"Rigor mortis had set in," a source told The Sun, "indicating she is likely to have been dead for anything up to six hours."
Police sources told the UK newspaper that there were no signs of drugs at the house.
A source told The People that the singer bought cocaine, ecstasy, ketamine and possibly heroin that Friday night.
"Amy seemed determined to have a big one on Friday night," the source said. "She was out in Camden on Friday evening, but seemed determined to carry on the party back at her flat.
"None of us know who was with her into the early hours of Saturday. But getting out of it was clearly her main priority of the night."
Amy's family told The Sun these reports were "nonsense."
Winehouse's close friend Kelly Osbourne was shocked by Amy's death, and did not believe there was any immediate cause for concern.
"I was speaking to her last night, she seemed absolutely fine, I don't understand how this could have happened," Osbourne told the Mirror.
Amy had seen a doctor on Friday evening, and she received a clean bill of health.
She had been getting regular checkups because of the overall toll her lifestyle had been taking on her body.
"The doctor was happy with her condition," a source told The Sun. "When he left on Friday night he had no concerns. Less than 24 hours later she was found dead."
"Amy was on her own at home apart from a security guard who we had appointed to help look after her over the past couple of years," PR rep Chris Goodman told The Sun.
"At this stage no one knows how she died. She died alone in bed."
Amy saw her mother, Janis Winehouse, the day before she died, and Janis was concerned for her well-being - as she often was.
"She seemed out of it. But her passing so suddenly still hasn't hit me." Still, Janis Winehouse told the Mirror that it was "only a matter of time" before tragedy took her young daughter.
Winehouse's father, a jazz musician and part-time taxi driver, was in New York City when he heard of his daughter's death. He had been scheduled to perform at the famous Blue Note jazz club. In what may have been Amy's last public comment, she wrote "I'm very proud of my dad," in an email to the New York Post on Friday.
Her father, who immediately returned to London upon hearing the news, is "devasted" by the loss.
A few days before her death, Mitch Winehouse also spoke to the New York Post about his daughter.
"Frankly she's had her ups and downs," he said.
"Our family has been left bereft by the loss of Amy, a wonderful daughter, sister, niece," Amy's family said in a statement.
An autopsy is scheduled for Monday, although it could take weeks before an toxicology report is complete.