Jacinda Ardern told reporters Sonny Bill Williams asked her if she was planning on expanding her family at an All Blacks training yesterday.
"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," the Prime Minister told reporters in Japan today.
Ms Ardern said the All Blacks have "prepared well" for the game against the Springboks 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."
Williams has been named on the bench for the All Blacks in their match against South Africa tonight in Yokohama.