Singer Amy Winehouse has been found dead at her flat.
The 27-year-old was discovered at the property in north London by emergency services at around 3.54pm this afternoon, according to sources.
It is understood her death is being treated as "unexplained".
The Back To Black artist cancelled all tour dates and engagements last month after a series of erratic public appearances.
She had been troubled by drink and drugs problems throughout her career.
The London Ambulance Service attended her flat this afternoon but were unable to save her life, sources said.
Celebrities paid tribute to the star on Twitter.
Radio DJ Fearne Cotton said: "Can not believe the news. Amy was a special girl. The saddest news."
Singer and presenter Myleene Klass wrote: "OMG. Amy Winehouse. Exceptional talent and really nice lady. RIP."
Presenter Phillip Schofield added: "Just heard the sad news that Amy Winehouse has died. At only 27 what a terrible waste of a great talent. Sincere condolences to her family."
Singer and radio presenter Emma Bunton said: "Such sad news about Amy Winehouse. My thoughts are with her family."
The troubled singer made her last public appearance on Wednesday night when she joined her goddaughter Dionne Bromfield on stage at The Roundhouse in Camden.
The singer danced with Bromfield and encouraged the audience to buy her album in the impromptu appearance before leaving the stage.
London Ambulance Service said it was called to the flat in Camden Square at 3.54pm.
Two ambulance crews arrived at the scene within five minutes and a cycle responder also attended, according to a spokeswoman.
"Sadly the patient had died," she added.
Winehouse joins the notorious "27 Club" of musicians who have died at that age after struggling to cope with fame.
They include Rolling Stone Brian Jones, who drowned in a swimming pool in 1969; guitarist Jimi Hendrix, who choked to death in 1970 after mixing wine with sleeping pills; and singer Janis Joplin, who suffered a suspected heroin overdose the same year.
Doors star Jim Morrison, who died of heart failure in 1971, and Nirvana front man Kurt Cobain, who shot himself in 1994, are also members.
A section of the road where the singer lived remained cordoned off tonight.
Journalists, local residents and fans gathered at the police tapes.
Forensic officers were seen going in and out of the building.
Fans began to lay flowers at the edge of the police cordon.
Jann Meyer, 33, who lives nearby, said he saw Winehouse around quite often.
"It's not really a shock, it was to be expected sooner or later. She was 27, and all good rock stars go at 27. She was very talented, she was amazing."
Another neighbour, who did not want to be named, said she saw the singer's grief-stricken boyfriend on the ground outside the house.
Two women then came "speeding" up in a black Mercedes and walked in and out of the house crying.
They said they believed the singer was at home last night.
Ron Brand, who had known Winehouse for about three years, said: "It's a tragic loss. She was beautiful, talented of course, and gentle. I loved her."
Mr Brand, father of comedian Russell Brand, said he believed she was no longer on drugs.
Winehouse's father, Mitch, is understood to be returning to the UK from New York.
He had been due to perform at the Blue Note jazz club in the city on Monday.
A message has been placed on the club's website, reading: "We are very sad to report that the Mitch Winehouse performance on Monday July 25th is cancelled due to the unexpected death of his daughter, Amy Winehouse.
"Our condolences go out to Mitch and his family."
A spokesman for the late singer said: "Everyone involved with Amy is shocked and devastated. Our thoughts are with her family and friends. The family will issue a statement when ready."
He confirmed that Winehouse's father, Mitch, was aware of his daughter's death and was on his way back from New York.