TOKYO, Sept 3 (Reuters) - Japanese shares soared on Friday, with the broad Topix index hitting a three-decade high, after Prime Minister Yoshihide Suga offered to resign, opening the way for a fresh government that could help the ruling party win an upcoming election. Nikkei share average rose 1.7% to 29,020, reaching its highest level since June, while the Topix vaulted as much as 1.7% to 2,017.00, reaching a level last seen in April 1991. The market has been rallying this week on hopes for a stronger government ahead of a ruling party leadership race and a general election later this year. Kyodo News reported Suga will step down and party sources said he would not run in a ruling party leader race in September, setting the stage for his replacement after just one year in office. (Reporting by Hideyuki Sano; Editing by Shounak Dasgupta) Our Standards: The Thomson Reuters Trust Principles.