HONG KONG — Rex Tillerson’s call for China to be denied access to its artificial islands in the South China Sea, made Wednesday at his confirmation hearing for secretary of state, set the stage for a possible crisis between the world’s two biggest economies should his comments become US policy.

Tillerson told the Senate Foreign Relations Committee that China’s multibillion-dollar island-building campaign in the oil-and-gas rich sea was illegal and “akin to Russia’s taking of Crimea.’’

“We’re going to have to send China a clear signal that, first, the island-building stops,’’ Tillerson said. “And second, your access to those islands also is not going to be allowed.’’

Should those words be translated into action after Donald Trump assumes the presidency Jan. 20, it would be a remarkable change in the US approach to Beijing’s island-building. China asserts sovereignty over most of the South China Sea, despite competing claims by countries including Vietnam and the Philippines and an international ruling rejecting most of Beijing’s assertions.

The Obama administration has challenged what it calls China’s “excessive maritime claims’’ by sailing warships close to the artificial islands, some of which feature deep harbors and runways capable of handling jumbo jets. But that has not stopped China from continuing its buildup, which includes military installations such as radar stations on more than 3,000 acres of artificial land built on reefs and shoals.

Tillerson’s comments garnered reactions including confusion, disbelief, and warlike threats from analysts in China.

“This is a signal, now that Trump is set to take office, that he wants to have a tough stand on China,’’ said Yang Chengjun, a retired senior colonel and military expert, who said China’s potential war-fighting capability was greater than the United States’. “China does not stir up troubles but we are not afraid of them when they come.’’

Lu Kang, a spokesman for the Chinese Foreign Ministry, declined to say what Beijing might do if the US Navy moved to deny China access to the islands, saying it was a “hypothetical question.’’

But his reaction also highlighted the confusion sown by the testimony, because Tillerson did not explain how the United States could block China from the islands. “I can’t predict what Mr. Tillerson is thinking specifically, and on the other hand, it is impossible for me to make any prediction about China’s policy, based on your assumptions of what he said,’’ Lu said.

That confusion was shared by one of China’s most prominent experts on the South China Sea, who also questioned the legality of any US effort to block access to the islands.

“Is this a warning? Or will this be a policy option?’’ said Zhu Feng, executive director of the China Center for Collaborative Studies of the South China Sea at Nanjing University. “If this is a policy option, this will not be able to block China’s access to these constructed islands. There is no legal basis.’’