Duncan also fears a trade backlash, referring to China being New Zealand's biggest trading partner.
Peter Thompson, chief executive of Barfoot & Thompson which sells one in three Auckland houses, said Labour's policy wouldn't solve the housing affordability issue.
"The reason prices are going up is lack of supply. We need more building, to free up building processes and free up more land," Thompson said.
Twenty out of Barfoot's top 25 agents were of Asian ethnicity but they worked harder than many other agents, he said, estimating only 3 per cent to 5 per cent of buyers were foreign.
Countries which banned foreign investors did not enjoy lower house prices and New Zealand did not have to follow other countries on the issue.
Thompson backs Reserve Bank moves on loan-to-value ratios, saying some people borrowed too much and this change was positive.
Shearer said first-time buyers were struggling to get on the housing ladder, partly because 2600 homes were sold to foreign speculators who had no intention of living in New Zealand. This figure was based on a voluntary survey of 549 real estate agents which found that 9 per cent of sales went to overseas buyers.