OTTAWA (Reuters) - Canada needs to take measures to ensure more people can afford housing at a time when prices are rising, particularly in cities like Vancouver and Toronto, Prime Minister Justin Trudeau said on Thursday, but gave no details.

Canadian governments have tightened mortgage regulations five times since 2008 in a bid to cool a housing market boom fueled partly by low interest rates.

Trudeau is facing calls for his Liberal government to do more amid concerns that markets such as Vancouver and Toronto are becoming over-valued.

"This is a very significant crisis ... we know that we need to take measures so that the affordability of homes is accessible for more Canadians", Trudeau told a televised news conference in Vancouver. He singled out Vancouver and Toronto as areas of concern.

Trudeau said last week that the government had to be careful, since whatever action it took would affect the entire country and not just the two big cities.

The Bank of Canada issued an unusually blunt warning on June 9, saying the rapid pace of home price increases in Toronto and Vancouver was unlikely to continue and adding the potential for a downturn was growing.

Canadian home prices rose 1.8 percent in May from a month earlier, and were up 9.0 percent from the year before, according to data released on Tuesday.

(Reporting by David Ljunggren, editing by G Crosse and Chizu Nomiyama)