Japan should be aware of the quickly changing economic environment in Asia, where China is fast emerging as an economic power and Southeast Asian countries are starting to doubt Japan's ability for regional economic leadership, the visiting chairman of the Singapore Institute of International Affairs said Wednesday.

"Japan's decade-long . . . no or slow growth has many people in Southeast Asia question the ability of Japan to really lead in economic terms," Simon Tay said during a lecture in Tokyo.

He pointed out that the recent decision by the Association of Southeast Asian Nations to negotiate a free-trade agreement with China shows a fundamental change in the mind of ASEAN countries.