Japanese Prime Minister Shinzo Abe said he would dissolve parliament's lower house on Thursday for a snap election, as he seeks a fresh mandate to overcome "a national crisis".

Abe, in power for five years, said he needed a mandate to shift some revenues from a planned future tax hike to social spending such as education, besides seeking support for a tough stance toward North Korea's repeated missile and nuclear tests.

"I will dissolve the lower house on September 28," Abe told a nationally televised news conference today.

Earlier, the head of Abe's junior coalition partner, Natsuo Yamaguchi, said he understood the election would be held on October 22.

The decision is largely seen as aimed at taking advantage of Abe's recently improved support ratings and opposition disarray.

Abe, whose ratings have risen to around 50% from around 30% in July, is gambling his ruling bloc can keep its lower house majority even if it loses the two-thirds "super majority" needed to achieve his long-held goal of revising the post-war pacifist constitution to clarify the military's role.

A weekend survey by the Nikkei business daily survey showed 44% of voters planned to vote for Abe's Liberal Democratic Party (LDP) versus 8% for the main opposition Democratic Party and another 8% for a new party launched by popular Tokyo Governor Yuriko Koike.

Abe's image as a strong leader has bolstered his ratings amid rising tension over North Korea's nuclear arms and missile programmes and overshadowed opposition criticism of the premier for suspected cronyism scandals that had eroded his support.

Some critics say Abe has risked creating a political vacuum at a time of rising geopolitical tension over North Korea.

And, given the unexpected results seen in other major developed countries, political analysts are not ruling out a "nasty surprise" for the Japanese leader.

"Abe's big gamble could yield a big surprise," veteran independent political analysts Minoru Morita said.