Updated

Hundreds of candidates have taken to the streets as the official 12-day campaigning for Japan's Oct. 22 lower house election began, with Prime Minister Shinzo Abe's ruling party facing challenges from regrouped opposition forces.

Up for grabs are 465 seats in the more powerful of Japan's two-chamber parliament.

Abe on Tuesday pledged his party's stable leadership as he sought voters' support for his measures on North Korea's missile threat and Japan's aging. Experts say he timed his call for an election when opposition parties were unprepared to solidify his grip within the party and extend his rule.

Abe's LDP and its coalition partner, Komei, are expected to win the majority, though a surging new group led by Tokyo Gov. Yuriko Koike is likely to take some seats away.