Australia's main national newspaper is facing a worldwide volley of criticism over an obituary calling the nation's most famous author "plain" and "overweight".

The Australian was slammed for referring to Colleen McCullough as 'fat and plain' in the opening paragraph of her obituary.

Australian author Colleen McCullough, whose 1977 best-selling novel The Thorn Birds became a smash hit television miniseries, has died at the age of 77.