Eric McIsaac at an appearance in Levin Court in relation to the death of his half-brother Alex Fisher.

Levin man Eric Baden McIsaac​ has admitted murdering his half-brother, 10-year-old Alex Fisher, at Waitarere Beach.

McIsaac, 26, entered a guilty plea to the charge in the High Court in Palmerston North on Thursday.

His mother cried in the public gallery while he was convicted and read his first strike warning by Justice Joe Williams.

Alex Fisher's body was found three days after he was murdered by his half-brother at Waitarere Beach.

According to court documents, McIsaac committed the murder at Waitarere Beach on either October 5 or 6.

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The search for Alex started on October 6, with the search concentrating on a forest near the beach.

WARWICK SMITH/FAIRFAX NZ Justice Joe Williams convicted Eric McIsaac of murder and read out his first strike warning.

Police initially said it was a missing person case, but were seen filling a car with items in evidence bags that afternoon.

By October 8, more than 100 people were searching for Alex. His body was found in the Waitarere Beach sand dunes later that day.

McIsaac was charged with the murder on November 11.

MAARTEN HOLL/ FAIRFAX NZ Family and supporters of Alex Fisher, 10, leaving the High Court in Palmerston North after Eric McIsaac pleaded guilty to murder.

McIsaac also pleaded guilty to the burglary of a Waitarere Beach property between September 26 and October 6, and unlawful possession of a knife in Waitarere Beach on October 6.

Before the hearing started, the judge thanked the family for showing up in "extraordinary circumstances".

"I salute your courage."

Media were banned from filming or photographing McIsaac, and from describing his appearance.

The judge remanded McIsaac in custody until July for sentencing.