Rugby in New Zealand is to undergo an extensive review, with the sport's bosses admitting on Friday the game was "under pressure" as it faces an All Blacks slump in world rankings and dwindling numbers at the grassroots level.

The five Super Rugby franchises and 26 provincial unions have announced a joint review aimed at setting the sport up "for sustained success over the next decade".

"It is timely to review how we deliver rugby and ensure the sport has the resources to ensure it is sustainable and relevant to fans and communities right across the rugby system," New Zealand Rugby (NZR) said in a statement.

Although rugby has long been treated almost like a national religion in New Zealand, with the All Blacks captaincy regarded by many as the most important job in the country, it is now struggling to maintain its support.

The fading prestige was not helped last year when the three-times world champion All Blacks were beaten in the semi-finals at the World Cup and along the way lost their 10-year grip on the No 1 world ranking.

In Super Rugby, an increasing number of players not immediately in line for All Blacks selection are being lured off-shore by big-money contracts on offer in Europe and Japan.

The next tier down, the national provincial championship, once the pinnacle for non-internationals, is now largely filled with little-known talents as it competes with All Blacks commitments and Super Rugby players undergoing off-season injury rehabilitation.

At a grassroots level, the number of women is surging but men, particularly in the 13-20 age bracket, are dwindling.

New Zealand rugby chief executive Mark Robinson said that while rugby in New Zealand had a structure that had served it well for more than 125 years, the time was right to look at how it can best thrive in a rapidly changing society.

"Rugby is under pressure in many parts of the game, from participation, fan engagement, talent retention and increasingly tough financial environments," he said.

"We have seen significant growth in rugby since professionalism in 1996, but not all areas of the game have thrived in that environment and there is a never-ending drive to grow revenue and manage the cost base of the game."

NZR has already announced changes at under-age level where, if a team cannot muster 15 players, a match can be played with a minimum of 10 players a side.

Games can be from 40 to 80 minutes long, with rolling substitutes across all grades, scrums can be uncontested, and at the learner level there will be no knock-ons.