Forensic search for William Tyrrell in NSW

NSW Police say they have not given up on finding out what happened to William Tyrrell

Nearly four years after William Tyrrell disappeared from his grandmother's yard, police will carry out a fresh search for the missing boy in bushland on the mid-north coast of NSW.

Detectives on Wednesday will begin a four-week forensic sweep around the property where he was last seen in Kendall, near Port Macquarie on September 12, 2014.

The initial search focused only on finding William and was not carried out with a view of deliberate human intervention, NSW Police said in a statement.

William was playing in the yard of his grandmother's home, aged three, when he vanished.

Hundreds of locals and emergency services workers spent 10 days looking for him in the rural township, forests, creeks and paddocks.

But they found no trace of William.

Detectives have been investigating the circumstances of his disappearance for the past four years, launching a special strike force led by the homicide squad.

The new large-scale search will be co-ordinated by search experts from NSW Police's public order and riot squad.

In 2016, the NSW government announced an unprecedented $1 million for information leading to William's recovery.