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There was speculation the winner could be on holiday or may not have seen coverage of the jackpot, which happened the night Hamilton celebrated its 150th birthday.
The spokeswoman said the winner was missing out on $2000 a day in interest - already totalling $10,000.
"We calculated it a couple of days ago based on current interest rates and it's roughly about $2000 a day."
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She said it was unusual for a winner to take so long to come forward and the Lotteries Commission believed the lucky punter probably did not know about their windfall.
"By this stage they're missing out on quite a considerable amount of interest. We have to speculate that they perhaps just don't know."
Meanwhile, this week's Big Wednesday winner from Auckland, who takes home $9 million in cash and luxury prizes, came forward yesterday. The jackpot had not been won since August.