Five candidates vying to lead Japan's top opposition party, and possibly become the next prime minister, are calling for Japan to get tough with China in an escalating territorial dispute.

The candidates — including former Prime Minister Shinzo Abe, former Defense Minister Shigeru Ishiba and party secretary general Nobuteru Ishihara — slammed China in a debate Saturday ahead of the Liberal Democratic Party's presidential election, scheduled for Sept. 26.

They called for Japan to bolster its control of disputed East China Sea islands, saying they are Japan's inviolable sovereign territory. They also discussed Japan's sagging economy and its plan to phase out nuclear power.

Analysts believe the LDP could win big in upcoming parliamentary elections. If it does, whoever wins the party leadership race could become Japan's next prime minister.