SAN FRANCISCO >> For a century and a half, San Francisco’s Chinatown, the nation’s oldest, has sheltered waves of immigrants seeking a new life.

It’s the birthplace of Chinese America, and to some extent, the broader Asian America that descended from immigration over the Pacific Ocean throughout the 19th and 20th centuries.

Now, Chinatown faces powerful economic and demographic challenges that could upend its identity as the city undergoes an unprecedented growth in tech jobs.

Rising rent elsewhere in the city has entrepreneurs eyeing Chinatown for offices, entertainment and housing. A $1.6 billion subway set to open in 2019 could provide an economic boost, bringing customers from outside while taking residents out to jobs. But speedier transit also brings added development pressures, especially in a pocket of the city coveted for its location.

At the same time, many Chinese Americans have scattered across the Bay Area, reducing the customer base of San Francisco’s historic Chinese center. Banquet houses that once hosted celebrations are closed, with some making way for modern restaurants and others sitting empty.

Can the birthplace of Chinese America maintain its heart in the midst of a race for space?

"It is the last frontier, when you think about it," said Bertrand Pellegrin, a brand specialist with the firm b. on brand who is interested in helping preserve the neighborhood. "It is one of the last central places downtown that has not been completely gentrified and overdeveloped."

Some civic leaders say traditional values and zoning regulations should protect the neighborhood of 15,000 to 18,000 people against too much development. Plus, they say, who would want to put a tech startup company in an older building without elevators or commercial janitorial service?

Others say, however, that younger generations of property owners may take the money from the rising land values and run.

"The northeastern waterfront has always been the biggest battleground for property and development because it’s so beautiful. The battle has always been to limit growth," said Howard Wong, a founder of a group opposed to the subway construction. "A huge transit development will make that situation worse."

And Chinatown leaders don’t even agree on what the district should be, other than a gateway for immigrants and destination for tourists.

Take 1920c, a fledgling co-sharing business launched in April, which offers work space to freelancers and to socially conscious startups. The people who bounded into the sunny yellow space one recent morning were young, plugged into wireless devices and, in many cases, not Chinese.

The influential Chinatown Community Development Center protested the business, saying its use violates zoning laws, which allows for retail and restaurants and certain professional services. Gen Fujioka, the center’s policy director, said the neighborhood "is not intended for tech offices."

1920c co-founder Jenny Chan, a 25-year-old woman who moved from Hong Kong 15 years ago, bristled over characterizations that she is callously gentrifying the neighborhood. Her business offers coding classes for girls and art shows to benefit renters groups, she said.

"They accused me of not fitting into the fabric of Chinatown," Chan said. "But my sign downstairs is in Chinese."

Longtime merchant Betty Louie said Chan is exactly what Chinatown needs: young professionals who love the alleys and old buildings and can inject vibrancy to the place.

"I want our ABCs to come back and be proud of their roots," said Louie, using the shorthand for American-born Chinese. "Really, for some of them, this is their Chinese village."

That’s why she recruited well-known San Francisco chef Brandon Jew to set up a new restaurant in Chinatown. Likewise, Chinatown real estate broker Pius Lee has championed restaurateur George Chen, who is opening a food hall and high-end restaurant in a multistory building where the popular dim sum palace Gold Mountain once stood. It will be called China Live.

Chen, who noted the coming subway factored into his decision, said he is all too aware that he’s dealing with space sacred to old-timers.

"Everyone says, ‘Oh my God. You just took over Gold Mountain. What’re you going to do? It’s not going to be a giant Starbucks, is it?’ " Chen said. "All we’re doing is adding a little more of a modern flavor."

Diners new to Chinatown will walk with the immigrants who still come across the Pacific.

Li Miao Er, a 53-year-old former seamstress, moved from China a year ago with her husband and daughter, now 21.

Li crosses a narrow street strung with colorful lanterns and walks to a corner market to buy greens. She speaks no English and fears taking the bus outside of Chinatown.

She dreams of a couch because after cooking and cleaning for others all day, she just wants to stretch out. She’d like two rooms so her daughter could have privacy. She’d like to save up to buy a house.

But, through an interpreter, Li expressed a feeling shared by many immigrants before her, no matter how homesick.

"It’s better here," she said, "than where I came from."