Reuters reports that the Bank of Japan bought exchange-traded funds (ETFs) on Friday for the first time this month as Tokyo stock prices slumped.

The central bank last bought ETFs on Jan. 28 and held off buying more as Japan's share prices hit their highest in three decades in line with a global stock market rally.

The fact it stepped in on Friday, when Japan's Nikkei suffered its biggest one-day fall since April, underscored the bank's new approach of intervening only when markets become volatile, analysts said.

The BOJ bought 5 million yen ($47,068) worth of ETFs on Friday, central bank data showed.

Its policy at the moment is to buy ETFs at an average annual pace of roughly 6 trillion yen, a commitment that forces it to keep buying even when stocks are booming.

Some analysts saw the BOJ's moves in February as a prelude to what may come out of a March review of its policy tools to make its asset-buying programme more nimble.