The doubling does not include the visitors who have bought local pre-paid SIM cards to put in their overseas phones.
Foreign credit card spending in the country has also been tracking about a third higher than last year - an extra $10 million a week.
A Rugby World Cup spokesman said little analysis was yet available about exactly how many visitors were here, but their influx could be easily seen.
"The proof is in the pudding and we see it in the crowds - though most Kiwis like to be Irish, it would seem," the spokesman said.
A surge of visitors this week was predicted in the preliminary forecasts released by the Tourism Strategy Group last year - when total visitor numbers were estimated at 85,000, 11 per cent lower than revised estimates of 95,000.
The forecasts had already picked that Argentinian crowds would be increasing by 63 per cent while Scottish visitors would be starting to go home.
Scotland narrowly missed out on a quarter-finals place to Argentina after losing to England at the weekend.
The quarter-finals have been split between Auckland and Wellington, with the All Blacks, Argentina, England and France playing in the former and Australia, South Africa, Ireland and Wales in the latter.
The total visitors forecast for the Auckland teams is about 16,000, including expat Kiwis - and 17,000 for Wellington.
Lingering rugby visitors from other countries push the overall figure near 40,000.
About 20,000 other rugby fans were expected to have arrived and already departed - many of them Australian visitors.
Airport, airline and immigration figures for September will be released later in the month.
