The three-day trip comes with Beijing and Washington at loggerheads over militarisation in the South China Sea, while at the same time trying to find common ground on how to deal with North Korea's nuclear and missile programmes in the wake of Pyongyang's latest tests.
Last week China confirmed that it has "weapons" on Woody Island in the disputed Paracels chain.
A US official told AFP that Beijing has deployed surface- to-air missiles on the island, apparently HQ-9s, which have a range of about 200 kilometres.
China opposes the proposed Terminal High Altitude Area Defence System (THAAD), with foreign ministry spokeswoman Hua Chunying warning today that it should not be used as a front to "undermine China's own legitimate (security) interests".
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The move comes in response to Pyongyang's launch of the Kwangmyongsong-4 satellite, which most in the international community viewed as a disguised ballistic missile test, violating multiple UN resolutions banning it from the use of ballistic technology.
The rocket came just a month after the North's fourth nuclear test.
"After the DPRK's nuclear test and satellite launch, we support the UN Security Council in passing new and effective resolutions against the DPRK," she told a regular briefing, referring to North Korea.
Tensions in the South China Sea - through which a third of the world's oil passes - have mounted in recent months after China transformed contested reefs in the Spratly islands further south than the Paracels into artificial islands capable of supporting military facilities.
"China deploying necessary national defence facilities on its own territory is no different from the US deploying defence facilities on Hawaii," she added.
China controls all of the Paracels, though Hanoi and Taipei have overlapping claims.