The police national dive team has joined the Catlins search for missing 11-year-old Mike Zhao-Beckenridge and his stepfather, John Beckenridge.

The Wellington-based dive team spent a short time near Curio Bay yesterday, but left the area about 6pm because conditions were too rough, search co-ordinator Sergeant Ian Martin, of Invercargill, said.

''They didn't really get an opportunity. It was just too rough for them to get into the water.''

The dive team would reassess their options today, he said.

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A helicopter has joined police, 20 LandSAR crew and volunteers in the search from Haldane to north of ''the Brothers'' near Tautuku.

Items of interest related to the search were found in the Catlins during the weekend, but police were tight-lipped about what they were and how they linked to the pair.

Mike Zhao-Beckenridge. Photo / supplied
Mike Zhao-Beckenridge. Photo / supplied

''There were a few things that have been picked up, but nothing significant,'' Sgt Martin said.

''We'll sit down and go through what has been found and where and reassess what we can do tomorrow.''

It was understood police were keeping an open mind about the location of the pair and their fate.

''While we do have an area of interest we are looking into, there is still no confirmation that Mike or John are still there,'' Southland area commander Inspector Kelvin Lloyd said yesterday.

''We are continuing to work with the current situation that Mike and John could be anywhere in the lower South Island region and we ask members of the public who may have seen Mike or John to contact us immediately.

''We also would like to hear from anyone who has information that might help us to locate them.''

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Sgt Martin said smaller teams would search ''areas of significance'' today, but he could not comment further as it was considered a criminal investigation.

The pair have been missing since March 13.

Mr Beckenridge is Mike's estranged stepfather and their contact is in breach of a parenting order, police say.

The pair were last seen near Slope Point in the Catlins on March 16. A farmer told police he spotted the pair in remote bush in the Catlins.

Police staff carried out an extensive search in the Haldane and Tokanui areas in Southland, Detective Sergeant Mark McCloy, of Southland police, said.

Items of interest in relation to the search were found in the Curio Bay area on Sunday and had been examined by police.

''We really want to resolve this situation,'' Det Sgt McCloy said.

''We understand that John may have grievances about a recent Family Court decision in relation to a parenting order but the current situation is not the best way to resolve things.

''John can call me via (03) 471-4800 at any stage and talk with me personally about his situation.

''We understand that John and Mike have a good relationship so we are keen to work to resolve this.''

John Beckenridge is also known as John Robert Lundh, Knut Goran Roland Lundh, or John Bradford.

The pair are thought to be travelling in a dark blue Volkswagen Touareg station wagon, with the registration number DUY263.

Mike is 1.65m tall, of solid build and of Asian descent. John Beckenridge is 1.75m tall, of medium build and of Swedish descent.

If anyone sees the pair they should contact police on 111 immediately.

Anyone with information that might assist in locating the pair should contact the Southern District Command Centre on (03) 471-5002.