Outside Parliament, Mr Shearer rejected suggestions the policy was rushed out to boost Labour after a slump in the past two polls, saying it had been formed over the past four months. The next major poll is One News, due on Sunday night.
He rejected claims that the policy was xenophobic.
"These are people who are speculating. We want to give first-home buyers the best opportunity."
He said he had received a significant amount of feedback on the policy, all of which was supportive.
"It's about standing up for first-home buyers and I am fed up with [Prime Minister] John Key talking the big talk, but no walk.
"There is nothing he is putting up to help those young couples."
Mr Shearer said policing the policy was not difficult and where trusts were used to buy properties, the beneficiaries of the trusts could be checked.
Mr Key tried to pour cold water on suggestions that restrictions on foreign buyers and a capital gains tax were effective in Australia, saying its homes were even less affordable that in New Zealand.
He said National's own plans of increasing land supply and speeding up resource consent processes would have more impact than Labour's proposals.
He said between 1999 and 2008, when Labour was in Government, the median sale price had increased by 100 per cent from $169,000 to $340,000. Under National since 2008, it had risen by 12 per cent.
However, Mr Shearer said Labour's suggested measures had slowed the house price increases in Australia.
The policies
National
* Build 39,000 homes in Auckland in accord with Auckland Council.
* Increase land supply, including potential government intervention if councils lag.
* Streamline resource consent processes.
Labour
* Prevent non-resident foreigners from buying property.
* Build 100,000 homes for first home buyers over 10 years.
* Introduce capital gains tax on all but the family home.
