TORONTO -- Ontario's finance minister can't say whether a tax on foreign buyers -- a centrepiece of his new package of housing measures -- will have an effect on the red-hot Greater Toronto Area market.

When asked what data the decision to implement such a tax was based on, Charles Sousa cited a November 2016 Toronto Real Estate Board survey that suggested foreign buyers were involved in about five per cent of purchases.

The board said that shows the amount of foreign buying in the Greater Toronto Area is minimal and not detrimental to the housing market.

Sousa says the question now is will the government's foreign buyer tax have an effect.

Ontario started collecting citizenship data on home purchases this week, and Sousa says now the government will assess what impact foreign investment is having.

In the Greater Toronto Area, the average price of detached houses rose to $1.21 million last month, up 33.4 per cent from a year ago.