Best-selling Australian author Colleen McCullough, whose novel "The Thorn Birds" sold 30 million copies worldwide, has died at age 77 after a long illness.

HarperCollins Australia publishing director Shona Martyn said McCullough died Thursday in a hospital on remote Norfolk Island.

Martyn said McCullough had continued producing books despite a string of health and eyesight problems by using dictation.

McCullough wrote 25 novels through her career. Her first novel "Tim" was published in 1974, and her final book "Bittersweet" was released in 2013.

Before becoming an author, McCullough studied neuroscience and spent 10 years as a researcher at Yale Medical School in the United States. She established the neurophysiology department at Sydney's Royal North Shore Hospital.

She is survived by her husband, Ric Robinson.