Southeast Asian leaders arrived in Tokyo on Wednesday to participate in a two-day summit with Japan that will focus on trade and security.
Thursday's gathering will be the first such meeting to be held outside the Association of Southeast Asian Nations region.
Prime Minister Junichiro Koizumi and ASEAN leaders are expected to ink Friday a joint declaration featuring the creation of an East Asian Community and a joint activity plan, which includes development projects in the Mekong River area.