World leaders were joining Ukrainian President Volodymyr Zelensky in Switzerland on Saturday for a summit on peace in his country, but with Russia staying away it is seen as the first step in a long process.

The Swiss hosts have sought to temper expectations at the two-day gathering, with an agenda laying the groundwork for a path to peace – with future summits envisioned, eventually involving Moscow.

But Zelensky himself expressed high hopes for the outcome.

"We will see history being made here at the summit," he said on social media platform Telegram, as he greeted presidents and prime ministers arriving at the luxury Burgenstock resort high above Lake Lucerne.

"Together, we are making the first step toward just peace based on the UN Charter and fundamental principles of international law," he said on X, formerly Twitter.

But in a combative speech on Friday, Russian President Vladimir Putin slammed the conference and demanded that Kyiv effectively surrender before any actual peace negotiations.

Zelensky branded Putin's demands a territorial "ultimatum" reminiscent of Nazi Germany's dictator Adolf Hitler, while Nato and the United States also immediately rejected the hardline conditions.

The conference, convening exactly 100 countries and global institutions, comes at a perilous moment for exhausted Ukrainians and outgunned soldiers, more than two years since Moscow launched its full-scale assault in February 2022.

More than 50 heads of state and government figure among the attendees, including all of the G7 leaders who have been meeting in Italy – with one notable exception.

US President Joe Biden instead sent his Vice President Kamala Harris, who announced more than US$1.5 billion in new aid for Ukraine, mainly for its energy sector and in humanitarian assistance as she arrived in a US Army helicopter.

The leaders of Britain, Canada, France, Germany, Italy and Japan are attending, as is the European Union chief and the leaders of Colombia, Chile, Finland, Ghana, Kenya and Poland.

Argentinian President Javier Milei and the presidents of Ecuador and Fiji were among the early arrivals.

Russia's Brics allies Brazil and South Africa are meanwhile only sending an envoy, and India will be represented at the ministerial level.

China is absent, insisting it will not take part without Moscow's presence.

After almost a year of stalemate, Ukraine was forced to abandon dozens of frontline settlements this spring, with Russian troops holding a significant advantage in manpower and resources.

Near Ukraine's embattled eastern front, hopes for any major breakthrough are nearly nil.

"I'd like to hope that it will bring some changes in the future. But, as experience shows, nothing comes of it," said Maksym, a tank commander the Donetsk region.

And in Kyiv, Victoria, a 36-year-old energy industry worker, said she was "exhausted" by the war and wanted to believe the summit would help end it.

But, she said, "I'm a realist in life, so I don't have high hopes."

Experts have also warned against unrealistic expectations from the gathering.

"Meaningful negotiations that could truly end the devastating war in Ukraine remain out of reach, as both Kyiv and Moscow stick to theories of victory that amount to outlasting the other," the International Crisis Group think tank said.

The summit aims to find paths towards a lasting peace for Ukraine based on international law and the United Nations Charter; a possible framework to achieve this goal; and a roadmap as to how both parties could come together in a future peace process.

A plenary session involving all delegations will be held on Saturday.

On Sunday, three topics will be discussed in detail in working groups: nuclear safety, freedom of navigation and food security, and humanitarian aspects.

A second summit is envisaged. Zelensky's chief of staff Andriy Yermak said on Tuesday that Kyiv hoped Russia would attend and receive a "joint plan" presented by the other attendees.

Samuel Charap, a Russia expert at the Rand think tank, said of the Burgenstock summit: "Russia is clearly going out of its way to demonstrate its pique with it... That tells you something.

"Avoiding the expansion of the pro-Ukraine coalition – they're concerned about this," he said.

Since mid-May, Russian military progress has slowed and Zelensky hopes to swing the momentum further with the back-to-back G7 and peace summits.

Zelensky arrived at Burgenstock on Friday evening after the G7 summit agreed to offer a new US$50-billion loan for Ukraine, using profits from the interest on frozen Russian assets.

A landmark 10-year security deal signed by Zelensky and Biden on Thursday will see the United States provide Ukraine with military aid and training.

Also on Friday, the European Union's 27 member states agreed "in principle" on beginning accession negotiations with Ukraine. (AFP)