Wellington - As the All Blacks chase a third straight Rugby World Cup in Japan, the schoolboy rugby competitions that forged many of New Zealand's stars face an "alarming" fall in player numbers amid concerns about elite schools poaching top talent.

Schoolboy rugby is a big deal in New Zealand - senior matches are televised nationally and the rivalries between some schools date back more than a century.

Before Jonah Lomu, Richie McCaw and Dan Carter became All Blacks legends, they were honing their skills for Wesley College, Otago Boys' High and Christchurch Boys' High respectively.

The prestigious Auckland Grammar boasts that 51 All Blacks have emerged from its rugby programme, while Christchurch Boys' High (46) and Wellington College (35) have similar pedigrees.

"It's part of the fabric of New Zealand society, rugby in all walks of life is, and certainly we've got strong traditions in our schools," said Peter Gall, who co-authored an independent report into secondary schools rugby released earlier this year.

The report, commissioned by New Zealand Rugby, found that while the game was booming among schoolgirls, boys were increasingly turning to alternative sports such as basketball.

"The numbers of boys playing the game at secondary school is trending downwards at an alarming rate, especially considering the overall secondary school roll has been steadily increasing," the report said.

"Decreasing numbers of players leads to fewer teams and problems in forming meaningful, viable competitions."

Figures from School Sport NZ show the number of schoolboy rugby players declined from 25 841 in 2014 to 21 532 in 2018, a fall of 17 percent.

Over the same period, basketball's popularity surged 41 percent from 13 130 to 18 498 participants.

In Auckland, the number of secondary school rugby teams fell from 225 to 181 between 2013 and 2018, a trend Gall said was echoed nationwide.

The report pointed to a range of reasons for the decline, including the "fragmented and confusing" structure of schoolboy competitions, a lack of qualified coaches and concern over the physical nature of the game.

It also said the hyper-competitive nature of the sport, with schools running rugby programmes akin to semi-professional academies, was "creating disquiet and questionable outcomes".

The report's release came shortly after controversy blew up in the Auckland 1A competition, when schools threatened to boycott St Kentigern College over its recruitment policies.

The row highlighted many of the concerns in Gall's report, with the wealthy private school accused of using scholarships to lure top talent that delivered it five titles in seven years.

"They're not building from the ground up, from year nine to 11. They're going after the superstars and it's brazen," Napier Boys' High principal Matthew Bertram said at the time.

St Kentigern eventually backed down and signed a code of conduct imposing conditions on player recruitment. But Gall said the issue was not confined to one school.

Students cited in the report said that a win-at-all-costs mentality had detracted from their enjoyment of rugby.

Gall said a major problem was in-fighting between schools, clubs and provincial unions over control of schoolboy competitions.

He said without good governance it was difficult to adopt policies to make the game more inclusive, encourage participation and place emphasis on values, rather than just winning.

"It can't be done on an ad hoc basis, there needs to be more planning and strategic thinking about how to grow the game," he said.

"There needs to be a lot more cooperation... and less self-interest.

"There's some provinces where the clubs are at war with each other and at war with the school and the schools are at war with the clubs and the provincial union. That can't go on."

In response to the report, New Zealand Rugby has appointed a secondary schools manager and is formulating a new structure to oversee how the game is run.

Gall said one benefit of maintaining a healthy schoolboy rugby scene was the conveyor belt of talent for the All Blacks and other New Zealand teams.

"Rugby's still a big sport and has a large following, it's not like it's going to fall over," he said.

"It will always be there at schoolboy level but, saying that, by building up the base of the pyramid with greater participation rates you're creating more opportunities for the cream to rise to the top."