"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.