According to the bank's data, 66% of customers were ahead on repayments at the end of June, up from 65% at the end of February, prior to lockdown.
The bank says the median customer was 9.2 months ahead on repayments, or $9,521 ahead of the curve, compared to 8.6 months, or $8,693, in February.
Westpac says this has pushed the customer "mortgage buffer" to $401 million.
Westpac NZ's general manager of consumer banking and wealth, Gina Dellabarca said: "Covid-19 has caused real financial difficulty for some of our home loan customers through no fault of their own, and we have a great team working to support them through these challenging times.
"However, this data shows another group of New Zealanders were not affected to the same degree, and together managed to put millions of dollars more towards their mortgages as spending opportunities disappeared during lockdown."
According to Dellabarca, repayments during lockdown were the highest in Nelson (median – $1,745), Wellington ($1,660) and Auckland ($1,482). The nationwide median was $828.
"Normally the increase in extra mortgage repayments is incremental so it’s great to see the numbers leaping forward," Dellabarca added.
The data indicates many New Zealanders in a stronger financial position invested surplus funds into their mortgages.
Yet borrowers who have lost their jobs and income remain on mortgage deferrals and payment holidays.
Finance Minister Grant Robertson has indicated that the Government and Reserve Bank will extend the mortgage holiday programme for vulnerable borrowers.
Deferral and holiday requests continue to pour in. In the week to July 17, 887 NZ loans were restructured to interest-only terms, while 407 customers requested complete payment deferrals.
