The New Zealand dollar and interest rates are both falling.
The kiwi dollar is trading at just under 63 US cents - the lowest it's been since June 2009.
It's being sold off as concern grows about the weakening world economy.
Meanwhile the New Zealand Reserve Bank is expected to cut the official cash rate by 25 basis points to 2.75 percent on Thursday.
But some banks aren't waiting until then to lower their rates.
The BNZ is the latest to move. It has cut its one-year mortgage rate to 4.35 percent. Customers must have a 20 percent deposit and do their other banking with BNZ.
One mortgage advisor told 3 News it's possible that some mortgage rates could fall below 4 percent by the end of the year.
Watch the video for the full report.