In China, a crowd of startups is looking to cash in on a hot real-estate market by disrupting the way apartments are rented.

As property prices have soared in Beijing, Shanghai and other large cities in recent years, many young workers and new graduates have been squeezed into renting spaces within apartments—and that is where “apartment operators” have stepped in. These companies sign long-term leases with landlords and sublease to individuals, typically after renovating and partitioning, though they also sublet entire apartments....