Barack Obama and Xi Jinping have headed to a desert oasis for an unusually relaxed US-China summit as the two presidents looked to forge a bond that could shape relations for years.
Allegations that China has waged a cyber-hacking campaign against the United States are likely to dominate the talks, which will also take up the constant trade niggles that have soured ties between the world's two largest economies.
But Obama also has a wider purpose -- trying to glean the strategic vision of the man set to guide a fast-growing China through the rest of his own presidency, with major effects on Obama's own foreign policy legacy.
The summit at the sun-scorched Sunnylands retreat in California marks Xi's first visit to the United States since he assumed power in March. US-based China watchers have voiced surprise at how quickly Xi has consolidated power.
The 59-year-old holds credibility as the son of one of China's founding revolutionaries and speaks in a confident, free-flowing style, a shift from the stilted formality of his predecessor Hu Jintao that frustrated the White House.
The two leaders had not been expected to meet until the G20 summit in Russia in September. But both sides, sensing uncertainty seeping into a complicated and often difficult relationship, saw value in an earlier encounter.
White House spokesman Josh Earnest said that Obama wanted "an informal atmosphere" and hoped "to see if there are broader opportunities for us to expand those issues on which we cooperate."
Obama and Xi are due to meet at 0000 GMT for formal talks and a working dinner. They will meet again on Saturday morning.
The White House is predicting no breakthroughs -- in part due to the casual nature of the meeting but also because the issues confronting the two leaders are so acute.
Blunt exchanges are expected on cyber security, following a string of reports that China-based operations have stolen huge troves of US military and commercial secrets.
China has signaled that it believes it too is a victim of cyber espionage. In troublesome optics for Obama, the summit comes as he faces criticism over revelations that the United States has run a massive Internet and telephone surveillance program for security purposes.
The White House rejected charges that the scandal weakened Obama's hand and instead said that the row showed how the United States holds vibrant discussions on individual rights.
"This is a pretty good illustration of the type of conversation we want to have about respecting civil liberties and protecting the constitutional rights of the people that you govern," Earnest said.
In a bid to ensure cyber security does not overshadow this summit, the two sides have already announced they will hold working group level talks on the issue in July.
North Korea will also come up, with US officials encouraged at signs that China is becoming impatient with Pyongyang's saber-rattling.
On the eve of the summit, North Korea and US-allied South Korea agreed to resume dialogue following months of soaring tensions.
Xi will be interested to hear Obama explain his signature diplomatic priority of ramping up the US presence to Asia -- a so-called "pivot" policy that many Chinese see as a bid to contain Beijing's rise.
Xi has called for a "new type of great power relationship" and -- in a sign that China can also focus on Washington's backyard -- visited Mexico, Costa Rica and Trinidad and Tobago before coming to California.
Several hundred protesters jeered Xi outside of the tightly guarded vacation compound, including members of the banned Falungong spiritual movement and Tibetans who chanted, "China, get out of Tibet!"
Advocacy groups have pressed Obama to urge the release of 16 key prisoners, hoping that the summit will give Xi a specific target on human rights.
"President Obama should stop the trade-centered diplomacy and instead make it a human rights-centered diplomacy," said Chen Guangcheng, the blind activist who escaped house arrest for the US embassy in Beijing last year.
Hours ahead of the summit, Chen's brother said that China had granted passports to him and his mother so that they could see Chen Guangcheng.
John Frisbie, president of the US-China Business Council, said the talks were 50 percent successful already just for taking place at this early date.
"Depending on how this weekend goes, the next step... might be an annual presidential summit," he said.
