Japan's ruling Democratic Party has formally kicked off a leadership race to pick the next prime minister.
The successor to Prime Minister Naoto Kan, who resigned as Democratic Party of Japan leader on Friday after months of criticism, faces a mountain of challenges.
A resurgent yen threatens exports and there is a major rebuilding job in the wake of March's devastating earthquake and tsunami.
A new, non-nuclear energy policy has to be shaped while ending the world's worst nuclear crisis since Chernobyl.
And the government has to find funds to pay for bulging social welfare costs, while reining in public debt already twice the size of the $US5 trillion economy.
Five men, including finance minister Yoshihiko Noda, trade minister Banri Kaieda and former foreign minister Seiji Maehara, have registered to run in Monday's party vote.