China's relationship with the US is "stable" despite tensions in the South China Sea, President Xi Jinping told top American diplomat John Kerry Sunday, adding that the Pacific Ocean is "vast enough" for both powers, state media said.

Xi met with Kerry in Beijing as tensions between the world's two biggest economies mount over Chinese island-building in strategic but disputed waters.

The United States is weighing sending warships and surveillance aircraft within 12 nautical miles -- the normal territorial zone around natural land -- of artificial islands that Beijing is building in the South China Sea.

Such a deployment could lead to a standoff on the high seas in an area home to vital global shipping lanes.

Beijing regards almost the whole of the South China Sea as its own, and satellite images show China is rapidly building an airstrip on an artificial island in the Spratly archipelago, which is also claimed in whole or part by US ally the Philippines, and Vietnam, among others.

But on Sunday Xi told Kerry that, "in my view", relations between the two countries "have remained stable on the whole", according to state-run news agency Xinhua.

"The broad Pacific Ocean is vast enough to embrace both China and the United States," Xi said.

He called for the two sides to handle disputes "in an appropriate way so that the general direction of the bilateral relationship will not be affected".

"The new type of China-US relationship has witnessed early harvest," he added.

Xinhua said Kerry, who arrived in China Saturday, "echoed" Xi's evaluation of bilateral ties before the two met for talks behind closed doors.

Chinese leaders had been defiant in talks with Kerry on Saturday, with foreign minister Wang Yi telling him that Beijing was "unshakeable" in its defence of sovereignty.

Kerry appeared less assertive in public, saying at a press conference Saturday that Washington was "concerned about the pace and scope of China's land reclamation".

He urged Beijing to "take actions that will join with everyone to reduce tensions".

Senior State Department officials had said ahead of the meeting that Kerry would take a tough line and "leave his Chinese interlocutors in absolutely no doubt that the United States remains committed to maintaining freedom of navigation".

An American naval commander has dubbed Beijing's massive land reclamation effort as China's "great wall of sand".

Xi is due to pay a state visit to the United States in September, and Xinhua said he looked forward to discussing bilateral ties with US President Barack Obama in a "candid and in-depth way".

Kerry flew to Seoul in South Korea later Sunday.