HO CHI MINH CITY, Vietnam—With the U.S. and China tangled in a nasty trade fight, this should be Vietnam’s time to shine. Instead, it is becoming increasingly clear that it will be years, if ever, before this Southeast Asian nation and other aspiring manufacturing destinations are ready to replace China as the world’s factory floor.

The specialized supply chains that made China a production powerhouse for smartphones and aluminum ladders and vacuum cleaners and dining tables are nowhere near as developed in Vietnam. Factories with U.S.-focused safety certifications and capital-intensive machinery aren’t as easy to find.

And Vietnam, with less than one-tenth China’s population, is already running into labor shortages as global manufacturers rush to set up shop here to avoid U.S. tariffs.

“China has a 15-year head start—whatever you want, someone’s doing it,” said Wing Xu, the operations director for Omnidex Group, which helps make large pumps for Pennsylvania-based industrial equipment manufacturer McLanahan Corp.

Omnidex has shifted some production to Vietnam, but out of more than 80 parts of a pump used in mining operations, factories here have been able to begin work on only 20 so far because molds must be created from scratch.