New Prime Minister Yoshihide Suga last month announced Japan would aim to cut emissions to net zero by 2050.
Japanese MPs have declared a climate emergency in a vote aimed at increasing pressure for action to combat global warming after the government last month committed to a firm timetable for net-zero emissions.
With the symbolic vote on Thursday by parliament's powerful lower chamber, Japan - the world's fifth-biggest carbon emitter - joins fellow Group of Seven members Britain, Canada and France in similar resolutions, as well as the European Union as a bloc and nearly 2,000 regional and city authorities around the world.
Prime Minister Yoshihide Suga last month announced Japan would aim to cut greenhouse gas emissions to net zero by 2050, a major shift for the world's third-largest economy, which relies heavily on imported fossil fuels.
The emergency, non-binding declaration - drafted by a cross-party group of legislators - cites "unprecedented damage" from hurricanes, flooding and forest fires, exacerbated by climate change at home and abroad, and said the world faced a "climate crisis".
Ruling Liberal Democratic Party MP Yoshihisa Furukawa said the resolution was vital to show the world Japan was not lagging in the fight against global warming.
The government is developing measures including investment funds and tax incentives to push through changes needed to reach the net zero target, and could also open the way for Japan's nuclear industry to fire up again, nearly a decade after the Fukushima disaster shut down most reactors.
Mr Suga last month said Japan would "pursue nuclear power" along with introducing as much renewable energy as possible.
Still, scientists and activists warn that action is still lagging to meet the Paris Agreement target of curbing emissions enough to keep temperature rises to within 1.5C-2C of pre-industrial levels.
Prime Minister Scott Morrison told energy company executives in Tokyo this week Australia shares Japan's pledge for net zero emissions but it was too early to commit to a 2050 target date.
"Can I just say that Australia also shares an ambition for net zero emissions," Mr Morrison said. "But what we are focused on is how get there and (how) that can be achieved."
He said low emissions technologies would be an important part of the Australia-Japan relationship, with the first pilot shipment to Japan of hydrogen from Victoria due in March.