The deal had the imprint of a Hong Kong billionaire nicknamed “Superman” for his empire building. One of the tycoon’s companies, which for years has run two ports on the Panama Canal, had been thrust into a broader showdown between China and the United States.

So the billionaire, Li Ka-shing, got out of the firing line by notching a $19 billion deal to sell the business to a group of deep-pocketed American investors.

Or so it seemed.

China’s leaders are now threatening to stop Mr. Li and the company he controls, CK Hutchison, from seeing the deal through, accusing the conglomerate of betraying Beijing.

The face-off tests how far Xi Jinping, China’s top leader, is willing to go to exercise his control over business in Hong Kong.

A former British colony, Hong Kong was returned to China in 1997 with Beijing’s promise it would mostly leave the city to govern itself, allowing it to remain a bridge to China but keep a system of freewheeling capitalism. Mr. Li, as a Chinese entrepreneur who tapped investors in the West to build an empire that included property, shipping and telecommunications, embodied that distinction.