LONDON - Amy Winehouse's mother said the singer seemed unwell a day before she died, a British newspaper reported Sunday, while her family mourned the loss of "a wonderful daughter, sister, niece" and more tributes flowed in from fans and fellow performers.

A mound of flowers, messages and handwritten notes grew Sunday outside of the north London home where ambulance crews found the singer dead before they arrived on Saturday.

"RIP Never Forgotten," read one message, while another said "It's all right, love. Go now."

The Sunday Mirror quoted Janis Winehouse as saying she believed it was "only a matter of time" before her daughter died. The 27-year-old singer had publicly struggled with drug and alcohol abuse for years.

"She seemed out of it. But her passing so suddenly still hasn't hit me," Janis told the tabloid.

Police said the cause of her death is being treated as "unexplained," rejecting speculation that she died from a drug overdose as "inappropriate." The circumstances surrounding her death are not yet clear, but police said a post-mortem is expected Monday or Tuesday.

Her spokesman, Chris Goodman, confirmed Sunday that a security guard had found her body and called ambulance services.

"Our family has been left bereft by the loss of Amy, a wonderful daughter, sister, niece. She leaves a gaping hole in our lives," the family of the "Back to Black" singer said in a statement, and requested privacy.

In her short lifetime, Winehouse too often made headlines because of drug and alcohol abuse, eating disorders, destructive relationships and abortive performances.

Actor Russell Brand, a former drug addict, wrote a lengthy tribute to Winehouse, urging the media and public to change the way addiction is perceived - "not as a crime or a romantic affectation but as a disease that will kill."

"Winehouse and I shared an affliction, the disease of addiction," he wrote. "Addiction is a serious disease; it will end with jail, mental institutions or death."

Others, like American singer Carole King, whose song Will You Love Me Tomorrow was covered by Winehouse, recalled her small, but powerful body of recorded music.

"She did such a beautiful performance on it," King told the BBC, saying that she was grateful to the late singer for the recording. "I just really hope that she's found peace now wherever she is."

No information about funeral or burial was immediately available.