Leaders from the US, Germany, France, Italy, Britain and Canada are arriving in Japan for the G7 summit.
US President Joe Biden’s plane touched down at a military airport to the south of the host city, Hiroshima, in southern Japan, on Thursday.
German Chancellor Olaf Scholz also arrived on Thursday, before the official start of talks on Friday.
European Union leaders will also be at the meeting, as will Australian Prime Minister Anthony Albanese. He leaves for Japan later on Friday.
There was speculation Ukrainian President Volodymyr Zelensky might also travel to Japan for the summit. However, the Japanese government said Mr Zelensky would attend via video link, Japanese news agency Kyodo reported.
Earlier, statements from Mr Zelensky’s entourage raised the possibility the president might attend the meeting in person.
During a visit to Ukraine, Japanese Prime Minister Fumio Kishida had invited Mr Zelensky to take part via video link.
Japan holds the rotating G7 presidency.
Kyodo, citing Ihor Shovkva, the deputy head of the Ukrainian presidential office responsible for foreign policy, initially reported an in-person meeting between Mr Zelensky and the G7 heads of state and government would depend on the military situation.
The war in Ukraine, the state of the global economy, denuclearisation, and the West’s relationship with China will top the agenda of the leaders’ discussions.
The talks are being accompanied by extensive security measures.
Police said 24,000 security personnel from all over Japan would be on duty during the meeting, which continues until Sunday.
The Peace Memorial Park, which the heads of state and government will visit for the opening ceremony, has been cordoned off with a two-metre-high fence.
Access to the atomic bomb dome is also blocked.
The burnt-out building was damaged when the US dropped an atomic bomb on the city in 1945 at the end of World War II. It is now a symbol of peace and a testament to the horror of nuclear weapons.
Mr Scholz said on Thursday he expected the summit to send a clear signal against the use of nuclear weapons.
“This is a very symbolic place here,” he said.
“The nuclear catastrophe that was experienced here is a reminder to all of us that we must ensure that nuclear weapons are never used.”
Boats patrolled up and down the river around the Peace Park on Thursday.
Some 140 schools were closed due to severe traffic restrictions.
The tightened security measures come against the backdrop of a recent attack on Mr Kishida, in which he was unharmed.
His predecessor Shinzo Abe had been shot dead at an election rally a few months earlier.
