Heads of state and government from the United States, Britain, France, Germany, Italy, Canada and host Japan are meeting in Ise-Shima, a mountainous region about 300 kilometres (200 miles) southwest of Tokyo.
The group, including US President Barack Obama -- who is making a historic trip to the atomic-bombed city of Hiroshima on Friday -- visited Ise Jingu, a shrine complex that sits at the spiritual heart of Japan's native Shintoism.
Obama was the last to arrive at the leafy site under heavy security, a phalanx of black SUVs with tinted windows pulling up alongside a group of schoolchildren waving Japanese flags.
He then walked with Japanese Prime Minister Shinzo Abe along a curved wooden bridge as they approached the forested sanctuary.
In line with tradition, the site's buildings are regularly replaced, but the sprawling shrine is believed to have occupied the same spot for more than 2,000 years.
Abe's decision to take his counterparts to the site -- also a hotspot for domestic tourists -- has raised eyebrows among some critics, however, due to lingering nationalist overtones left over from when Shinto was the state religion.
The group will also get a brief crash course on Japan's world-leading green car technology later Thursday, with a series of bilateral meetings also scheduled.
Among them, Germany's Angela Merkel meets with Canadian Prime Minister Justin Trudeau, who is also holding talks with French leader Francois Hollande.
The sputtering global economy is expected to take centre stage when the formal talks get under way later Thursday, although divisions are likely to remain over whether the world should spend or save its way out of the malaise, with Japan and Germany at odds on the issue.
- 'Global crisis' -
China, the world's second-largest economy, will not be present, but a row over its territorial assertiveness in the South China Sea will loom large in the discussions.
Japan and the US are keen to corral support for a growing pushback against Beijing's claim to sovereignty over almost the whole of the South China Sea which has raised the ire of its smaller neighbours.
The refugee crisis will also feature on the group's packed schedule.
Speaking on the sidelines of the meeting, European Council President Donald Tusk said Thursday that the world needs to act together on the issue gripping Europe, and not leave the continent to battle the problem alone.
"We are aware that it is because of geography that the most responsibility is, and will continue to be, placed on Europe," Tusk told reporters.
"However we would also like the global community to show solidarity and recognise that this is a global crisis."
Last year, some 1.3 million refugees, mostly from conflict-ridden Syria and Iraq, asked for asylum in the European Union -- more than a third of them in Germany.
The G7 will also discuss Islamist terrorism, with France's Hollande keen to address the issue after a brutal 2015 that saw France hit twice by jihadists.
Security was tight across Japan, with thousands of extra police drafted in to patrol train stations and ferry terminals. Tokyo said it was taking no chances in the wake of terror attacks that struck Paris and Brussels in recent months.
Dustbins have been removed or sealed and coin-operated lockers blocked at train and subway stations in the capital and areas around the venue site. Authorities said they will be keeping a close eye on so-called "soft targets" such as theatres and stadiums.
Britain's referendum next month on whether or not to stay in the European Union is sure to figure prominently in discussions, as economists warn a so-called Brexit could dent the global economy.
Following the talks, Obama will move on to Hiroshima, becoming the first sitting US leader to travel to the city, the site of the world's first nuclear attack, on August 6, 1945.//AFP