Barack Obama and Theresa May have downplayed concerns that Britain becomes a lower trading priority for the US after Brexit
Leaders from the world's biggest economies are meeting in China today at the G20 summit.
They will be focusing on ways of boosting growth in the world economy.
UN Secretary General Ban Ki-moon said current Sustainable Development Goals aim "to leave no one behind" economically or socially, and called on developed economies to take more action to support developing ones.
"The G20 this year is going through a great transformation, moving from a short-term focus on managing global financial challenges to a long-term vision for sustainable development," he explained.
"We are now talking about the overall sustainable development where nobody, nobody among seven billion people, will be left behind, regardless of their socio-economic status, regardless of their ethnicity, and whatever their differences may be," he added.
On the eve of the the summit, US President Barack Obama and his Chinese counterpart Xi Jinping announced they were ratifying the Paris Agreement on climate change.
However, there have been tensions too over the issue of human rights in China.
President Obama said: "When I bring up issues like human rights, there are some tensions there that perhaps don't take place when President Xi meets with other leaders. But that's part of our job, that's part of what we do."
The visit is British prime minister Theresa May's first to China, and she met President Obama, Russian President Vladimir Putin and President Xi in bilateral meetings.
In a joint news conference with Mr Obama, the pair downplayed concerns that Britain becomes a lower trading priority for the US after Brexit.
The US has been negotiating a broad EU trade deal and said ahead of the Brexit vote that Britain would go to the back of a line for a two-country deal if it left the EU.
However, Mr Obama said he never said Britain would be punished.
"We're going to do everything we can to make sure that the consequences of the decision don't end up unravelling what is already a very strong and robust economic relationship that can become even stronger in the future," he said.
But he did say that it wouldn't make sense for America to lose focus on its European trade talks.
Mrs May will speak with world leaders about the implications of Brexit for world growth and Britain's place in the world.
She suggested that there is a global backlash against free trade, and political leaders have to do more to ensure everyone feels its benefits.
"I want us to be a global leader in free trade, but we can't ignore that as we look at the G20, which is about global economies and growth, we can't ignore the fact that there is sentiment out there in a number of countries which is anti-globalisation," she said.
"We need to consider how we can make sure that when we put these free trade arrangements in place, they're actually going to benefit everybody."
Mrs May will also meet the Australian Prime Minister Malcolm Turnbull on the sidelines of the summit.
Australia has promised to share its experience in negotiated free trade deals.
Mrs May will also meet the Prime Minister of India Narendra Modi, and the Deputy Crown Prince of Saudi Arabia Mohammad bin Salman Al Saud.