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

She died today in a hospital on remote Norfolk Island, HarperCollins Australia publishing director Shona Martyn said.

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

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

The Thorn Birds, published in 1977, was made into a hugely popular TV mini-series starring Richard Chamberlain.

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.