Simon Cowell has proclaimed Whitney Houston to be "one of the greatest superstars of all time".

The music mogul and 'x factor' judge is one of a number of high-profile stars to pay tribute to the 48-year-old singer - who died in a hotel room yesterday (11.02.12) - saying he was "devastated" by her passing.

He said: "You're going to remember where you were when you heard the news. It's that significant. I am absolutely devastated by this news. I am so sad for her.

"She was undoubtedly one of the greatest superstars of all time, one of the greatest voices in our life time we're likely ever to hear."

Mariah Carey - who previously worked with Whitney on song 'When You Believe'- said she was distraught by the passing of her "friend"

She wrote on twitter: "Heartbroken and in tears over the shocking death of my friend, the incomparable Ms. Whitney Houston. My heartfelt condolences to Whitney's family and to all her millions of fans throughout the world. She will never be forgotten as one of the greatest voices to ever grace the earth."

Dolly Parton, who allowed Whitney to cover her classic song 'I Will Always Love You', said she was "grateful" to her and added she would be missed "from the bottom" of her heart.

She said in a statement: "Mine is one of the millions of hearts broken over the death of Whitney Houston. I will always be grateful and in awe of the wonderful performance she did of my song, and I can truly say from the bottom of my heart, 'Whitney, I will always love you.' You will be missed."

Singer Kelly Rowland also recalled Whitney's "love and encouragement" she had shown when she first rose to fame with Destiny's Child in the late 90s.

She wrote on twitter: "I am beyond heartbroken. Whitney Houston was undoubtedly one of the greatest singers & performers of all time & such a huge influence of me. She embraced me when I first started out with Destiny's Child, with love, with encouragement and with that powerhouse voice.(sic)"

The reason for Whitney's death is as-yet unknown.