haha... once you are a nz tax resident, your oversea income (worldwide income) is taxable in nz.
if you declare your tax in nz as very little, then ird is interested to know where did you get your money from to buy those houses?
This is a taxation country, naive (act innocent) is not an excuse. Basically, ird can trace your ird number and match the houses you own and work out the tax that you need to pay + 150% penalty & interest + potential prosecution.
Overseas people can run away ( probably not in the country already), but people who are here for a long haul, your buying has to match your income source ( declared or under declared), and able to explain to ird your source (of fund) are taxable income in NZ. Any discrepancies will be a subject of interest for IRD.
Another misconception people hold on double tax arrangement.
If you hold a permanent resident - activities that follow, family move here, have family home/property here, the time you spend in NZ, IRD will hold you as a tax resident of nz and not of China's ( or other country). IRD has its own test of "permanent place and abode test" to deem a person as NZ tax resident hence subject to NZ tax regime. This is a well-developed area of tax law.
IRD is now spending a lot of money on its software, matching information from Land-on-line ( place your property titles are kept), immigration department ( when you are in and out of the country and your family information) and IRD's own records of your taxation activities. The information will give them a basis to audit and to visit you to have a chat ( or invite you to have a cup of coffee at IRD).