New Zealand Police is offering a $100,000 reward and potential immunity for information that will reveal what happened to missing two-year-old Amber-Lee Rose Cruickshank.

Amber-Lee was last seen on 17 October, 1992, at a Cornwall Street property in Kingston, on the shores of Lake Wakatipu.

Her family had left their home in Invercargill and were relocating to the West Coast.

"While we don’t know where she is or what happened, we believe she may have been the victim of foul play," says Detective Inspector Stu Harvey.

"There is someone out there who holds the key to the truth."

Amber-Lee and her family - her mother, stepfather and baby brother - had been staying at the Kingston address, catching up with friends.

A number of people were socialising at the property at the time she went missing.

"It has been nearly 29 years since she disappeared.

"We’re hoping with the passing of time that someone will come forward with information that will finally provide both Amber-Lee’s family and Police with answers."

Over the years Police has conducted a significant number of enquiries.

"We have gone to great lengths to explore different scenarios and investigation leads without success," Harvey says.

On May 5 this year Amber-Lee would have turned 31-years-old. 

"Her mother and family members have been left to worry and angst about what happened to this very young child for far too long.

"We want to bring them answers and closure."

Amber-Lee's mother and brothers spoke to the New Zealand Herald about the reward offer.

"Twenty-nine years of not knowing what happened to our beloved Amber-Lee has been 29 years of pain, anger, frustration and torment - with endless searching and praying for this nightmare to end," said mother Nicola Cruickshank.

"To have answers, to have closure, to have Amber-Lee come home - that's all we want.

"And now we are living in hope, praying that this reward will enough to entice whoever holds the key to the truth of Amber-Lee's disappearance and her whereabouts to come forward - whether she has passed, or is alive."

She's never given up hope her daughter would be found.

"We have done everything possible and within our power to find the answer," she told the Herald.

"I feel this reward is our last resort."

She appealed to anyone with any information to speak up.

"We are begging you to come forward and do the right thing," she implored.

"Put an end to this nightmare and bring Amber-Lee home - where she belongs.

"She deserves that much at least."

Police will pay out a reward of up to $100,000 for material information or evidence which leads to the identity and conviction of any person or people responsible for her disappearance.

The offer of a reward will remain in place for six months.

The Commissioner of Police will determine the amount of the reward and will, if necessary, apportion payment where there is more than one claimant.

Immunity from prosecution may be considered for any accomplice, not being the main offender, who provides information or evidence to Police.

Anyone with information is asked to contact Police via 105 and reference Operation Oliver: 921030/2144.