Westpac is the first of the major banks to impose the Reserve Bank's new investment lending restrictions.
From 4.30pm today, Westpac will not take new loan applications beyond the revised 60 percent loan-to-value ratio constraint.
From September, most loans to property investors across New Zealand will require a deposit of 40 percent. Those with a deposit of less than 40 percent will be limited to a five percent loan.
The change will also extend the current LVR restrictions from Auckland to around the country.
In a statement, Westpac said: "The new regulations announced yesterday are expected to come into effect in less than six weeks"
"There is a shorter transition period allowed for banks to meet the RBNZ's requirements than in 2013 and 2015 when there was a six month period to make all the necessary adjustments and comply."
Westpac also said it had already signalled it will work in the spirit of the new regulation.
"To do so, and given the period allowed for adjustment, we will not take new loan applications… from property investors from 4.30pm today."
Those with pre-approvals will still be assessed as per the usual process.