Breakthrough in search for Belinda Peisley

Women's clothing - including underwear matching the size of missing NSW mother Belinda Peisley - has been found buried beneath her former Blue Mountains home.

Police made the discovery on Monday, at the start of a fresh three-day forensic dig at the property in Katoomba.

Ms Peisley hasn't been seen since September 26, 1998. She was 19.

Detectives suspect she was murdered but her body has not been found, despite numerous ground searches and extensive investigations.

A 2013 inquest found she likely died around the time of her disappearance but could not determine the cause or circumstances of her death.

Forensic investigators on Monday found female clothing, including undergarments buried under the Katoomba house where Ms Peisley had lived.

Detective Chief Inspector Grant Taylor said the find was of "great interest".

"The undergarments are consistent with Belinda's clothing size," he said in a statement on Tuesday.

"We will await the results of the forensic analysis, which includes DNA testing, to determine whether new lines of inquiry can be explored."

Two years before the teenage mother-of-two disappeared she had inherited a large amount of money and bought the home in Katoomba's Trow Avenue.

But by the time she died Ms Peisley was a drug addict, in considerable debt and the only money coming into her account was welfare payments.

The last person to see her alive was a nurse at Blue Mountains Hospital.