More than 14,000 police and gendarmerie officers have been deployed to secure the event, outnumbering the town's 10,000 residents.
Lake Geneva is being patrolled by around 30 police boats equipped with anti-drone systems.
A no-fly zone has been imposed over the area and road restrictions have forced some local businesses to close temporarily.
Around 20,000 people marched in nearby Geneva ahead of the summit.
What began as a peaceful demonstration turned violent when some protesters attacked what they described as symbols of capitalism and global institutions.
A Tesla car was set on fire and windows were smashed at a United Nations office.
Police responded with tear gas.
The summit's agenda includes the aftermath of a preliminary US-Iran deal to end their conflict, the Russian war in Ukraine, global economic imbalances and reducing Western dependence on China for critical minerals.
The gathering is also overshadowed by tensions over US President Donald Trump's tariff threats and broader unease among allies about Washington's commitment to the international order.
French officials expressed relief that Trump will attend at all, after he left last year's G7 in Canada early.
The G7 brings together the leaders of the US, UK, France, Germany, Italy, Japan and Canada, alongside European Union representatives.
This year's summit, hosted by France as current G7 chair, also includes invited guests from Brazil, India, Kenya, South Korea, and – joining on Tuesday – Saudi Arabia, Egypt, Qatar and the United Arab Emirates.
On Wednesday, heads of major AI companies including Sam Altman of OpenAI, Dario Amodei of Anthropic and Demis Hassabis of Google DeepMind are expected to attend, as France looks to put artificial intelligence regulation and infrastructure on the agenda.
(ał)
Source: IAR, Reuters, PAP