OAKLAND — Giving a boost to Oakland’s ambitions to become a tech employment hub, ride-booking pioneer Uber Technologies is expanding its corporate operations to downtown Oakland and planning to fill a historic building with about 2,500 workers, the company announced Wednesday.

Starting in 2017, Uber employees will work in the old Sears Building, a now-vacant, 380,000-square-foot complex that fronts both Telegraph Avenue and Broadway, right above the 19th Street BART station.

“Uber is a game-changing company and this is a game changer for Oakland,” Mayor Libby Schaaf said during a City Hall event to formally announce the Uber expansion. “It solidifies our place as the center for urban innovation in America.”

High-tech companies now employ about 5,600 people in Oakland, according to a recent report by the Oakland Chamber of Commerce. That means that Uber by itself would increase the number of tech workers in Oakland by nearly 50 percent.

“The Uber deal marks a very dramatic shift for downtown Oakland,” said Sid Ewing, a senior vice president with Colliers International, a commercial realty brokerage. “This is a high-profile tech company going into Oakland and gives the downtown much more credibility.”

The Oakland building, now known as Uptown Station, includes 330,000 square feet of offices and 50,000 square feet of retail space. Uber also is planning another headquarters building of 423,000 square feet in San Francisco’s Mission Bay district.

At present, Uber has about 2,000 employees in the Bay Area, not including its contract drivers.

“This is a milestone not only for Oakland but for Uber Technologies,” said Renee Atwood, Uber’s global head of people and places. “The Bay Area is our hometown. We are proud our global headquarters is going to include Oakland.”

About 20 percent of Uber’s workforce now lives in the East Bay. Uber predicts that in about two years, about 25 percent of the company’s workforce will reside in the East Bay.

The Oakland offices will be a co-headquarters for Uber, since the company will retain all of its San Francisco facilities, even after it expands into Oakland. “Technologists, product developers, human resources, operations, sales, marketing and business development” will be among the kinds of employees at the corporate office in Oakland, said Adony Beniares, Uber’s director of real estate and facilities.

Oakland leaders and developers of Uptown Station for months have been seeking to attract a tech company from San Francisco or other locations to the historic building, which is close to dining, entertainment, arts and retail stores that make up the Uptown district, a cornerstone of a remarkable revival of downtown Oakland.

“We are excited to deepen our roots across the bay by investing in the revitalization of historic downtown Oakland and to become a permanent part of the fabric of the East Bay community by adding thousands of jobs at our Oakland site,” Atwood said.

In March, a gourmet market was announced as the first tenant for the structure. Uber said it will keep the ground-floor retail.

“We will support and invest in the ground-floor retail,” said Eva Behrend, an Uber spokeswoman. “We will encourage and support homegrown restaurants and retailers” for the first-floor spaces.

Scott Smithers, managing principal with Lane Partners, said the realty firm is “thrilled” and would continue to work with Uber to finish the building’s $40 million renovation now that the sale has been completed.

The building opened in 1929 as Capwell’s department store and was bought by Sears a few years after the 1989 Loma Prieta quake damaged the structure.

For Oakland, the deal could help spur more expansions of San Francisco companies and tech firms to the city’s downtown — a priority for the new mayor.

“We’re proud that Uber was attracted to Oakland’s creative energy, incredible talent, progressive values, prime location and accessibility to the entire region,” Schaaf said.

A number of development projects could be sparked by Uber, Colliers broker Ewing said. These include the 1100 Broadway building by SKS and a 23-story office tower at 601 12th Street in Oakland’s City Center by Shorenstein Properties. Ewing also is tracking two other prime sites in downtown Oakland.

“Uber is like a pebble hitting still water,” Ewing said. “You will see ripples throughout Oakland and the East Bay from this.”

Those ripples, though, may trigger higher housing, office and retail rents in Oakland. As more well-paid workers work and live in Oakland, that could force home prices and apartment rents higher.

“This is fantastic that Uber is expanding into Oakland,” City Councilwoman Lynette Gibson-McElhaney said in an interview Wednesday. But she also warned, “I’m concerned about the displacement that is already happening in Oakland.”

Thousands of residential units are in the pipeline, but thousands more are needed, and suburban cities in the East Bay must pitch in, Gibson-McElhaney said.

Uber also said it will scout for further expansion sites in Oakland’s downtown.

“Oakland is now part of the Uber world,” Beniares said.

Contact George Avalos at 408-859-5167. Follow him at Twitter.com/georgeavalos. Mike Blasky covers Oakland City Hall. Contact him at 510-208-6429. Follow him at Twitter.com/blasky.