Popular Osaka Mayor Toru Hashimoto formally launched a bid for national power on Wednesday with a new political party that critics say taps simmering nationalist sentiment just as Japan faces increasingly strained ties with China and South Korea.

"Our glorious country Japan has fallen into a state of decline," Hashimoto told a crowd of backers at a fundraising party in Osaka, western Japan, after announcing his local party would go national. "Let's fight together ... to once again revive a glorious Japan."

The beginning of Hashimoto's de facto campaign for a national election coincides with deepening disputes between Tokyo and Beijing and Seoul over islands in the region, feuds rooted in a legacy of resentment over Japan's wartime rule.

"He's definitely pushing Japanese political discourse further to the right, Koichi Nakano," a professor at Sophia University in Tokyo, said earlier. "A lot of Japanese are looking for a messiah who will turn things around and make everything wonderful."

Some opinion polls show that Hashimoto's Japan Restoration Party is more popular than the ruling Democratic Party of Japan.

In one survey, it ranked higher than the biggest opposition party.

Japan has had six premiers since 2006 as it struggles with an ageing population and fading competitiveness.