But now the main suspects are poverty and winter.

"Preliminary post-mortem findings suggest the woman's death is not suspicious," a police spokesman said on Wednesday.

"She may have died of hypothermia. It is believed she was sleeping rough."

Detective Inspector Frank Gilroy of Kuring Gai Local Area Command said the 50-year-old woman had been homeless, spending time in a nearby squat.

She was seen walking in the Berowra Valley Regional Park on Friday. On Friday night and early Saturday morning the temperature in Sydney fell to 7 degrees.

Her body was found the next day close to popular fishing ponds and rifle range, near the start of the Great Northern Walk to Newcastle.

Katherine McKernan, chief executive of Homelessness NSW, said authorities were aware of rough sleepers in the Hornsby bush as well as a swelling group along the Hawkesbury River.

"There's a large demand on crisis services and they are full," Ms McKernan said. "There's nowhere for people to be taken in."

A growing number of those turned away were older women, she said.

"Women are finding themselves, later in life, in poverty. We are finding that there are more homeless women as a result."

More than 28,000 people were homeless in NSW on the latest census night in 2011. In February, the latest Sydney survey found there were 365 people were on the streets.

The number of people without stable housing increased 32 per cent in the last two years.

Ms McKernan said there were no figures on deaths among the homeless but research showed rough sleepers died 20 years younger than members of the general population.