Jacinda Ardern has revealed the unusual question Sonny Bill Williams asked her at an All Blacks training on Friday.

Williams dwarfed the Prime Minister as she greeted the All Blacks at the captain's run at Tatsuminomori Seaside Park in Tokyo ahead of the Rugby World Cup opening ceremony and first game last night.

When questioned about her brief visit, Ardern told reporters Williams asked her if she was planning on expanding her family.

"I was just talking very briefly with Sonny Bill about preparation and he changed the conversation quite quickly. Look, he was trying to encourage us to expand our family. I was just encouraging him to win the game," Ardern told reporters in Japan today.


Williams later posted to Instagram about his encounter with the Prime Minister saying, "It was nice having you at training @jacindaardern. But even better having a yarn with you about having more children".

Ardern said the All Blacks looked well prepared for the clash and were "feeling positive".

"I had a really quick chance to have a chat with them yesterday. From both what they've said and on the field their preparation has been good, they were feeling positive.

"You can see that they feel not just New Zealand behind them, but Japan the All Blacks here the focus on them, the promotion of them around Tokyo is incredible and you'd have to see it to believe it."

The All Blacks kick off their World Cup campaign tonight at 9:45 pm.

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