SAN JOSE — For the third time in nine months, a major new office center has broken ground in downtown San Jose, fresh evidence the city’s urban core no longer is an economic abyss when it comes to construction of new office towers or modern tech campuses.

Platform 16, a billion-dollar complex envisioned as a gleaming tech hub of three modern office buildings and featuring 16 terraces, began construction Wednesday.

“This is the first project to get a shovel in the ground in this part of the downtown,” San Jose Mayor Sam Liccardo said during the groundbreaking. “It will be the first of many.”

The tech campus of 1.1 million square feet will sprout on a huge site once dotted by a ramshackle collection of old offices, industrial yards, and vacant lots on the banks of the Guadalupe River in downtown San Jose, a short distance from the Diridon train station.

“Platform 16 emerges at the intersection of so many important downtown San Jose assets: the Guadalupe River Park, Mineta San Jose International Airport, the Shark Tank, and our central station,” the mayor said.

The notable amenities of the campus include 16 private outdoor terraces that will give people in the three office buildings unobstructed views of San Jose and its flanking mountain ranges, a cafe, and a big fitness and wellness center.

“This project is going to cost $1 billion to build,” said Bob Pester, an executive vice president with Boston Properties, the lead developer. “We hope Platform 16 will change the landscape of San Jose. San Jose is at the heart of the region’s innovation and growth.”

Platform 16’s principal owners are Boston Properties, with a 55 percent stake, and the Canada Pension Plan Investment Board, which has a 45 percent stake. TMG Partners and Valley Oak Partners, prior owners of the property, will assist Boston Properties with the development.

“More leading companies are choosing to call downtown San Jose home because of our world-class facilities and access to transportation,” said San Jose City Councilman Raul Peralez, whose district includes much of the downtown district.

From the Platform 16 project, tech workers will be able to swiftly reach a Target-anchored retail center, the SAP sports and entertainment complex, San Pedro Square, and the Diridon train station.

“For decades this has been a dead zone between the Target shopping center and the SAP Center,” Matthew Mahood, chief executive officer with the Silicon Valley Organization, said in an interview. “Platform 16 creates vibrancy in that dead zone. That’s going to start happening all over downtown.”

CBRE commercial real estate agents Sherman Chan, Mark Schmidt, Mike Charters, and Will Schmidt have begun to scout for one or more tenants at Platform 16. The brokers believe the campus is ideal for a big tech company. The project is bounded by Autumn Parkway, West Julian Street, North Autumn Street, and a railroad line, and is just south of a Target store that’s part of the bustling San Jose Market Center.

“Platform 16 is a first-in-class transit-oriented development right in the heart of Silicon Valley,” said Aaron Fenton, vice president of development with Boston Properties.

The first phase of the Platform 16 development consists of a modern office building totaling roughly 390,000 square feet, along with an underground parking garage.

The project represents the transformation of the western edges of downtown San Jose.

“For decades, the only thing of significance out here was the SAP Center,” Councilman Peralez said in an interview. “It was industrial yards or undeveloped land. Platform 16 is a first of its kind. We are transforming this undeveloped land with a massive commercial project.”

Once complete, the complex could accommodate 7,000 workers. Devcon is the general contractor that is constructing the project.

“Platform 16 creates a natural connection to the Target regional power center, to San Pedro Square, to the arena, to the Google project,” said Scott Knies, executive director of the San Jose Downtown Association. “The downtown is growing, with this addition in the northwest corner of the downtown.”

Google has proposed a transit village nearby called Downtown West near the Diridon train station. The search giant plans to employ 25,000 people in a mixed-use neighborhood of office buildings, hotels, homes, shops, restaurants, cultural hubs, entertainment centers, and open spaces.

“This is the new downtown,” Liccardo said, referring to the western edges of the city’s core. “It is exciting to watch. This project is part of the re-imagining of the downtown.”