China may take advantage of the Ukraine crisis and do something "provocative" in Asia while Western powers are focused on defusing tensions with Russia, a US general warned Wednesday.

Russia's deployment of more than 100,000 troops on Ukraine's border has triggered fears in Washington and other Western capitals of a looming invasion.

General Kenneth Wilsbach, the head of US Pacific Air Forces, noted that China had aligned itself with Russia in the crisis, raising questions about own intentions in Asia.

"From the standpoint of will China see what's happening in Europe and... try to do something here in the Indo-Pacific -- absolutely yes, that's a concern," Wilsbach said, using an alternative term for the Asia-Pacific region. "I do have my concerns that they would want to take advantage," he added, speaking to reporters on the sidelines of the Singapore Airshow.

"It won't be surprising if they tried something that may be provocative, and see how the international community reacts."

Wilsbach said that when Beijing expressed support for Russia in the Ukraine standoff, he held talks with his staff and other "entities" in the region about its implications.

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Based in Hawaii, Wilsbach's command would play a central role if conflict erupts in the Pacific.

Over the years, Beijing has been blamed for stoking tensions in the region as it has steadily cemented control of key islands and atolls in the South China Sea.

Beijing claims almost the entirety of the sea, but that overlaps with those of Taiwan and four Southeast Asian countries -- Brunei, Malaysia, the Philippines and Vietnam.

While the United States and other Western nations have no claims there, they fear Chinese control would infringe on freedom of navigation in the strategic waterway.

In recent months, China has also ramped up pressure on Taiwan -- which it sees as its territory -- by sending fighter jets into the island's air defence identification zone.

Wilsbach said that when China looks at crises, it considers whether "this is an opportunity for gain".

He did not go into specifics about what China might do during the Ukraine crisis, saying only that there were "probably a number of options" for Beijing.