Japanese voters went to the polls on Sunday for an election in which the ruling Liberal Democratic Party (LDP) was anticipated to receive a groundswell of support following the assassination of former Prime Minister Shinzo Abe, a leading statesman and party power broker.

Abe, Japan's longest-serving modern leader, was gunned down on Friday during a speech in support of a local candidate in the western city of Nara – a killing the political establishment condemned as an attack on democracy itself.

Elections for seats in the Japanese parliament's less powerful upper house are typically seen as a referendum on the sitting government, and the latest opinion polls already pointed to a strong showing for the ruling bloc led by Prime Minister Fumio Kishida – an Abe protege.

As the nation mourns, both the LDP and its junior coalition partner, Komeito, could gain from a potential wave of sympathy votes, political analysts said.

"The ruling LDP-Komeito coalition was already on course for a solid victory," James Brady of the Teneo consultancy said in a note. "A wave of sympathy votes now could boost the margin of victory."

Campaigning was halted on Friday after Abe's killing, but politicians resumed pre-election activities on Saturday.

There was an increased police presence when Kishida appeared at a campaign event in a city southwest of Tokyo and a metal detection scanner was installed at the venue – an unusual security measure in Japan.

Polls opened at 7am local time and were due to close at 8pm.

A strong showing at the polls could help Kishida consolidate his rule, giving the former banker from Hiroshima a chance to carry out his goal of boosting defence spending.

It might also allow him to revise Japan's pacifist constitution – something even the hawkish Abe was never able to achieve.

Opinion polls show a majority of voters favour greater military strength. (Reuters)