The biggest opposition group, the Constitutional Democratic Party of Japan is expected to gain seats but it may not be enough to topple Prime Minister Kishida's coalition.
Japanese voters have went to the polls to decide whether to endorse the conservative government of Fumio Kishida or weaken the new prime minister.
The vote on Sunday is seen as a test for Prime Minister Kishida, who called the election soon after taking the top post early this month.
Kishida's Liberal Democratic Party (LDP) has been battered by its perceived mishandling of the coronavirus pandemic.
Already, Kishida has struggled to advance policies to help poorer people, while securing a big boost in military spending and taking a harder line on China.
With his lacklustre image failing to inspire voters, the LDP is on the brink of losing its sole majority in the lower house of parliament for the first time since 2009, opinion polls show, although its coalition with junior partner Komeito is forecast to remain in control.
Japan's vaccination drive initially lagged other advanced nations. More than 70 percent of the population is now fully vaccinated and infections have dropped sharply, but some voters remain wary.
"It's hard to say the pandemic is completely snuffed out and society is stable, so we shouldn't have any big changes in coronavirus policy," said Naoki Okura, a doctor, after voting in Tokyo.
"Rather than demanding a change in government, I think we should demand continuity."
Several key LDP lawmakers are also facing particularly tough contests, including Akira Amari, the party's secretary general.
Turnout will be crucial, since higher turnout tends to favour the opposition.
Three hours after polls opened, turnout stood at 6.32 percent, down 0.83 point from the previous lower house poll - but 16.6 million voted in advance, the Internal Affairs Ministry said.