The Bank of Japan may maintain ultra-low rates for a further period of well over a year, governor Haruhiko Kuroda said, but warned against the idea of propping up the economy through unlimited money-printing to finance government spending.

The BOJ last month modified its forward guidance, or a pledge on how it will guide future monetary policy, to say it will maintain current very low interest rates at least until the spring of 2020.

"There's a good chance current low interest rates will be maintained beyond (the spring of 2020) depending on future developments," Kuroda said in a speech at a seminar.

"When we say we will keep rates low for an extended period of time, we mean it will be maintained for quite a long time," he said later in response to a question from the floor.

Kuroda said while Japan's economy continues to expand moderately, global growth was showing signs of weakness and hurting exports, output and manufacturers' business sentiment.