US President Joe Biden hailed his "most constructive" talks with Chinese President Xi Jinping Wednesday, as they agreed at their first summit in a year to restore military-to-military communications and ease tensions.

The leaders of the world's biggest economies shook hands and smiled as they met at a historic estate in California for their first talks in a year, and wrapped up the four-hour summit with a walk in the garden.

"I have just concluded several hours of meetings with President Xi and I believe they are some of the most constructive and productive discussions we've had," Biden told a press conference at the Filoli estate in California.

US Democrat Biden said that while he disagreed on many issues with the Chinese Communist leader, whom he has known since 2011, Xi had "just been straight" with him during the talks on Wednesday.

The move to restore a military hotline, which China severed after then US House speaker Nancy Pelosi visited Taiwan in 2022, was "critically important," he added.

"Miscalculations on either side can cause real, real trouble with a country like China," he said. "And so I think we're making real progress there."

But Xi and Biden remained far apart on the wider flashpoint of Taiwan, with the Chinese president telling his US counterpart to stop arming the island and saying that reunification was "unstoppable".

Beijing claims sovereignty over the self-ruling democracy and has not ruled out seizing it by force.

The two sides announced a host of other agreements, including that China had agreed to tackle the production of ingredients for the drug fentanyl, responsible for a deadly epidemic of opioid abuse in the United States, officials on both sides said after the talks.

They also agreed to hold talks on artificial intelligence, Chinese state media said.

- 'Veer into conflict' -

The two leaders had not met in person since they held talks in Bali in November 2022, and relations nosedived after the United States shot down an alleged Chinese spy balloon in February this year.

Since then, Beijing and Washington have been engaged in intense diplomacy to get the two leaders face to face.

Earlier, Biden said talks had gone "well" and raised two thumbs up while he and Xi both waved at reporters as they strolled side-by-side in the grounds of the scenic country estate.

"We have to ensure that competition does not veer into conflict," the US leader told Xi across a long wooden table as their delegations sat down for talks.

Xi responded by saying that "Planet Earth is big enough for the two countries to succeed."

"For two large countries like China and United States, turning their back on each other is not an option," he said.

After the initial session of talks and a working lunch of herbed ricotta ravioli and tarragon chicken with gold rice pilaf, Biden posted a brief update on X, formerly Twitter.

"I value the conversation I had today with President Xi because I think it's paramount that we understand each other clearly, leader to leader," Biden said.

"There are critical global challenges that demand our joint leadership. And today, we made real progress."

- Taiwan tensions -

But on Taiwan, the rhetoric seemed to have barely moved on.

China's foreign ministry said Xi had told Biden to "stop arming Taiwan and support China's peaceful reunification. China will realize reunification, and this is unstoppable."

Biden, meanwhile, urged Xi to "respect" upcoming elections in Taiwan, amid fears that the vote next year could become a new flashpoint, a US official said.

Russia, a partner of China in what Washington sees as a growing authoritarian alliance, welcomed the meeting, with the Kremlin calling the talks "important for everyone."

For his part, Xi was expected to push for an end to trade curbs, with the Chinese economy struggling to shore up growth after its tough zero-Covid policy.

The Chinese leader was to host a dinner with US executives after the summit.