Sources told the (Sydney) Daily Telegraph that a security guard in her upscale waterfront neighborhood in Wooloomooloo found her body early Saturday after a friend called building management.
Police said only that the circumstances of her death were "not suspicious." But Dawson, 47, had struggled for years with depression.
"She was in very bad shape. Terrible shape," a friend, who asked not to be identified, told the Telegraph. "She had failed to show up to a lunch a couple of days ago and then when I had seen she hadn't tweeted in almost a day it was clear something was wrong."
Actor Russell Crowe, a neighbor, was spotted weeping after learning of Dawson's death.
Dawson had been cut from "Next Top Model" after a cast shakeup, and friends said she was upset by the dismissal.
After being dogged by Internet trolls, Dawson became a campaigner against bullying. She also went public about her struggle with depression after a suicide attempt in 2012, discussing it in interviews and writing about it in a memoir, "Air Kiss and Tell."
Born in New Zealand, Dawson became a model in Europe and New York at the age of 16. She settled in Australia in her late 20s, continuing to work as a model and then becoming a popular TV personality in Australia and New Zealand.