After the man and woman's arrest at the property near Harden they were taken to Young Police Station where they were questioned by detectives.

Police announced on Wednesday afternoon they had charged the pair with Amber's murder.

"A man and woman have been charged with murder by Homicide Squad detectives investigating the suspicious disappearance of 19-year-old woman Amber Haigh, almost 20 years ago," a NSW Police spokesperson said.

"Amber was reported missing on Wednesday 19 June 2002, after she failed to return to her home at Kingsvale, where she and her six-month-old son had been living with a married couple."

Police were told the couple dropped Amber off at Campbelltown Train Station on Wednesday 5 June 2002, where she intended to travel by train to Mt Druitt to visit her sick father in hospital.

"Later that day, money was withdrawn from her bank account at an ATM on Queen Street, Campbelltown," the spokesperson said.

"Despite extensive investigations by police over the years - including numerous public appeals and a reward for information - Amber has not been located and the circumstances of her disappearance remain undetermined."

In 2011, a Coronial Inquest found Amber to be deceased, having died as a result of homicide or other misadventure in early June 2002.

"In 2020, a formal review of the case was conducted under the Homicide Squad's Unsolved Homicide framework and a re-investigation commenced by detectives attached to Strike Force Villamar II," Police said.

It was only last week, the NSW Police Force, together with the NSW Government, announced the reward for information relating to Amber's suspected murder had been increased to $1 million.

"As part of ongoing inquiries, strike force detectives travelled to Thurgoona and seized a white Suzuki Sierra for further forensic examination last Wednesday (28 April 2022)," the spokesperson said.

"Following extensive investigations, a man and woman, both aged 61, were arrested at a property at Harden about 7.30am today (Wednesday 4 May 2022)."

Police said a search warrant was executed at the property a short time later, where police seized a number of items relevant to investigations.

"The man and woman were both taken to Young Police Station and have since been charged with one count each of murder," Police said.

"Additionally, the man has been charged with aggravated sexual assault - victim with serious intellectual disability."

The pair were refused bail to appear at Cowra Local Court tomorrow (Thursday 5 May 2022).