Boris Johnson arrived in Cornwall for the gathering of some of the world's most developed economies, with climate change set to be high on the agenda.
A picture of the PM stepping off on a jet was posted on his Twitter account, alongside the caption: "I've arrived in Cornwall for this year's @G7 where I'll be asking my fellow leaders to rise to the challenge of beating the pandemic and building back better, fairer and greener.
"It will be a busy and important Summit, and I can't wait to get started."
Labour's shadow environment secretary Luke Pollard labelled the move "plane stupid".
"There's no train line from Cornwall to Washington or Tokyo but there is to London. The prime minister should have taken the train, not got a plane," he said.
Asked about his decision to fly into the summit, Mr Johnson said: "If you attack my arrival by plane, I respectfully point out that the UK is actually in the lead in developing sustainable aviation fuel.
"One of the points in the 10-point plan of our green industrial revolution is to get to jet zero as well as net zero."
Other world leaders arrived in Cornwall on Wednesday, with Joe Biden landing at RAF Mildenhall in Suffolk on Air Force One.
Rather than making the train journey from Paddington in London, Mr Johnson took the 250-mile (400km) trip from Stansted airport to Newquay in Cornwall.
Taking a plane creates almost five times more greenhouse gas emissions than the equivalent train journey, according to the government's own emission figures.
One of the key policy priorities of this year's summit is to "create a greener, more prosperous future".
The summit's website adds: "We will protect the future of our planet by moving to net zero and providing financial support for developing countries to do the same."
In November, Glasgow will host COP26, where parties are expected to commit to enhanced ambitions.