As the economy now slows, companies are increasingly running into financial trouble, with some having to borrow even more to pay their debts. Policy makers are worried that the country’s spiraling level of corporate debt could threaten the broader financial system.

Sunac, China’s seventh-largest property developer in terms of sales, has been able to tap into its financial strength to help companies under pressure. Since 2012, Sunac’s property sales have grown at double-digit rates nearly every year, giving it the firepower to scoop up assets and land plots.

Before the Wanda deal, Sunac in January pumped $2.2 billion into LeEco, a tech firm struggling to pay off its creditors. This May, it paid $1.5 billion for an 80 percent stake in Tianjin Xingyao, a property firm known for leaving its projects uncompleted.

In 2015, Sunac made a play to rescue Kaisa, pledging $1.2 billion to take over the troubled property company; it later pulled out after Kaisa did not meet certain conditions for the deal. That same year, it announced a partnership with the cash-poor Yurun Holding Group, which ran a business empire ranging from sausage making to property and finance.

It is a remarkable turnabout for the company’s founder, Sun Hongbin.

Mr. Sun started his career at the Lenovo Group, where he was promoted to run enterprise development. But he had a falling out with Liu Chuanzhi, the founder of Lenovo, over a business dispute. Related to the dispute, Mr. Sun was sentenced in 1992 to five years in jail for misappropriation of public funds.