Five lawmakers filed candidacies Friday to lead Japan's opposition party and possibly become prime minister following the next elections, calling for efforts to boost the country's economy and shore up its defense.

The opposition Liberal Democratic Party has ruled Japan for most of the time since World War II. Analysts are forecasting it likely will win the largest number of parliamentary seats in elections yet to be called, but it would likely need a coalition to gain majority control.

The party has been gaining in polls due to voter dissatisfaction with a perceived lack of leadership by the ruling Democratic Party of Japan, whose popularity has languished as the economic recovery has stalled and the government has struggled with the aftermath of last year's earthquake, tsunami and nuclear disasters.

In a televised debate Friday, the candidates called for rebuilding the economy and strengthening Japan's defense at a time of deepening tensions with China.

The sense of crisis sharpened after Chinese surveillance ships entered Japanese waters early Friday near disputed islands in the East China Sea, adding to tensions between the Asian powers.

The candidates are mostly political veterans, including former Prime Minister Shinzo Abe, former Foreign Minister Nobutake Machimura, former Defense Minister Shigeru Ishiba, LDP Secretary General Nobuteru Ishihara and former economic minister Yoshimasa Hayashi.