AN INTENSIVE month-long search to solve the mystery of a missing boy in a Spiderman suit has begun in NSW's Mid North Coast today - but it is understood that police are not expecting to find his remains.

William Tyrrell, then aged just three, vanished from his grandmother's property in Kendall on the NSW Mid North Coast on September 12, 2014.

He was playing in the yard of the home when he disappeared.

An extensive search shortly after involving hundreds of locals and emergency services workers spent 10 days looking for him, believing he was lost, but to no avail.

The missing boy has not been seen since.

But, this morning, dozens of riot squad officers, have arrived for their first day in a new month-long search. It is understood the search could lead to an inquest into the little boy's death.

But, this morning, dozens of riot squad officers, have arrived for their first day in a new month-long search. It is understood the search could lead to an inquest into the little boy's death.

Police have confirmed a deputy state coroner will visit the search site in coming days, to monitor the police operation which, it is understood, could the groundwork for an inquest to be held into the boy's disappearance.

NSW Police said detectives from Strike Force Rosann, formed to investigate William's disappearance, will begin the forensic search in bushland near the home.

Detective Chief Inspector Gary Jubelin told reporters NSW Police has "not given up on this investigation".

"I don't want this interpreted that the investigation is coming to an end," he said. "We're committed to finding out what's happened to William.

"We're mindful that it's over three-and-a-half years since William disappeared and we haven't solved the matter. We will continue on until we do solve this matter.

"I think based on what took place during the original search and from our investigations it's reasonable to draw the conclusion that William's disappearance as a result of human intervention and not through misadventure.

"The search we're conducting now and fairly extensive search is so we can produce that evidence whether it be a coroner's court or criminal court showing that William's disappearance is a result of human intervention and not through misadventure."

Mr Jubelin added the force has "grave concerns" over William's whereabouts.

"It's been a very long time," he said. "As I have said to the family and I can't be any more honest than what I say to the family in a situation like this: until we know conclusively that William is not alive we will treat it with the possibility that he is still alive. Obviously we still have grave concerns."

He confirmed police are in contact with the coroner's office in relation to the search and the death will go an inquest if police can't solve it from a criminal perspective.

"We've always considered the possibility of it going to an inquest," he said. "We're keeping

our minds open to that. I want to also stress we have numerous lines of inquiries including persons of interest that we will fully exhaust before the matter goes to the coroner. Of course it's up to the coroner."

He added there were "hundreds of persons of interest" in the case but very few "high risk" persons of interest.

"We have a lot of police going to be on the ground," he said on the Today show this morning. "What they are trying to do is shore up they are trying to do is shore up the fact that William Tyrrell is certainly not in that area, which will be crucial to any ongoing inquiry."

It is understood that police are not expecting a major breakthrough or a body. A coroner will be on the scene to inspect police work.

The operation is being be co-ordinated by search experts from NSW Police's public order and riot squad.

Officers from Sydney arrived in Port Macquarie on Tuesday ahead of the search, and are expected to detail further on Wednesday morning what they hope to find.

They plan to canvas areas already searched, and expand to new areas in an operation predicted to last three to four weeks.

It is not known what has triggered this latest search.

On the second anniversary of William's disappearance in 2016, the NSW government announced a $1 million reward for information leading to his recovery.

THE DISAPPEARANCE OF WILLIAM TYRRELL

2014

SEPTEMBER 12 - Dressed in a Spider-Man outfit, three-year-old William Tyrrell goes missing from the front yard of his foster grandmother's home in Kendall, 40km south of Port Macquarie.

SEPTEMBER 21 - Police halt the search for the missing boy after scouring surrounding bushland and neighbouring houses.

2015

JANUARY 20 - Police search the home and business of washing machine repairman William Spedding, who had been due to carry out repairs at the Kendall house at the time the boy disappeared.

JANUARY 23 - Spedding publicly denies any involvement in William's disappearance. No charges have been laid against him.

FEBRUARY 19 - Homicide detectives take over the case and say it's likely William was abducted.

MARCH 2 - Police search bushland near Bonny Hills for three days after a tip- off.

APRIL 17 - William's foster parents speak publicly for the first time in an emotional video released through police which does not identify them. On the same day, police say the boy may have been a victim of a paedophile ring.

SEPTEMBER 12 - "Where's William" week is launched one year after he disappeared.

2016

SEPTEMBER 12 - A $1 million reward is offered for information leading to William's return.

2017

AUGUST 24 - William's foster child status is revealed after a court ruling.

2018

JUNE 12 - NSW Police announce the start of a four-week forensic search of bushland in Kendall.

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