New Zealand has told international referees to "get fitter" in order to keep up with the pace of the modern game.

All Blacks assistant coach Wayne Smith delivered the message Wednesday ahead of the second Tri-Nations Test against South Africa, saying referees needed to be at peak fitness to meet the demands of Test rugby.

Smith's comments came after last week's first Test when 46-year-old Irish referee Alan Lewis appeared to struggle to keep up with play as New Zealand won 32-12.

Another Irishman, Alain Rolland, will control Saturday's Test at Wellington.

Smith said the fitness requirement was greater as top teams keep the ball in hand longer and kick less, reducing stoppages.

"The ball in play is around 40 minutes in the Test matches this year because of the way we're playing," he said.

"If you talk to our tight forwards, they'll talk about how the game has changed, markedly, because of the amount of running they have to do.

"Referees are going to need to make sure they're up there fitness-wise."

Smith previously advocated the use of two referees in Tests, while All Blacks head coach Graham Henry called for referee substitutes.

"The game is going in the direction people want it to go in," Smith said.

"There can't be too many complaints around from people watching the game at the moment.

"We just have to make sure that the fitness levels of everyone goes up so we can continue playing it."

SAPA-AP