In a surprise break with market principles, the Bank of Japan said Wednesday that it is considering purchasing stocks held by the nation's most troubled banks, effectively bolstering their financial standing and stock prices at its own expense.

Up for purchase are stocks in excess of core capital at over 10 major and regional banks, BOJ Gov. Masaru Hayami said in a news conference.

Although nothing concrete has been decided, the BOJ could retain these stocks -- worth roughly 7 trillion yen to 8 trillion yen -- for as long as 10 years, he said.