For the first time in more than a decade, Oakland’s skyline has a new office tower — and many more to come.

Last month, health insurer Blue Shield of California began moving 1,200 workers to 601 City Center, a 24-story building a few blocks west of the 12th Street/Oakland City Center BART Station.

The new high-rise has sweeping views of downtown Oakland, the Bay Bridge and the nonprofit’s old home, San Francisco, where it was headquartered for 80 years.

Blue Shield’s cross-bay move will result in major rent and tax savings, said Sandra Clarke, the company’s chief financial officer. Two-thirds of its employees already live in the East Bay and now have a better commute.

“San Francisco real estate is very expensive. We want to make the best use of our (health care) members’ money that we can,” she said. “The options that Oakland offers, especially in this downtown area, make it worth really serious consideration. I know we’re very happy that we made this decision.”

The new building has more light and air than Blue Shield’s former offices at 50 Beale St., a 1967 building that’s now dwarfed by newer towers next door occupied by Salesforce. The Oakland tower also has floor-to-ceiling windows, a gym and a roof deck.

A wave of migration from San Francisco, along with local business growth, has made Oakland one of the hottest local economies in the country. Additional office projects totaling more than 4 million square feet, or room for 20,000 more employees, are under construction or planned downtown, which currently has around 80,000 jobs.

More than a dozen major housing projects are also in progress. Combined with easy BART access and proximity to new restaurants and bars, downtown is seeing the biggest building boom in decades, experts say.

“The skyline’s going to be totally reimagined,” said Chris Roeder, a real estate broker at JLL. “The perception of Oakland has changed.”

Many of the new projects have already have full tenant commitments. Kaiser Permanente plans to build a $900 million headquarters that would be the largest office building in Oakland. BART plans to buy a renovated property at 2150 Webster St. for a new headquarters. One of its neighbors will be the Sierra Club, which moved to Oakland in 2016, after 124 years in San Francisco, to save on rent. San Francisco tech firms Square and Credit Karma have also signed major Oakland office expansions.

Morten Jensen, president of Oakland architecture firm JRDV, increasingly sees a “dual core” of major employment and housing centers in San Francisco and Oakland, connected by a 15-minute BART ride.

“I think we’re right at the tip of the iceberg of the potential of what can happen,” he said.

Jensen sees affordable housing as a daunting problem, but with BART being the lifeblood of local economic growth, he also wants to see regional leaders prioritize transit expansion.

“It’s time for Oakland to assume a larger role in the Bay Area. Transportation is really key to this,” Jensen said. “It’s not just Oakland by itself. It’s Oakland linking to the entire region.”

Officials are studying both a second transbay BART tube and second bridge across the bay, but there are disagreements over priorities.

Oakland is thinking bigger. Since 2015, the city has been working on a Downtown Plan that will guide growth over the next 20 years. The plan was restarted in 2017 to focus more on equity and benefits for existing residents, particularly marginalized communities of color.

A draft plan calls for 61,000 new jobs and nearly 30,000 new homes downtown, up to a quarter of them affordable, by 2040. The city could implement fees and require more affordable housing to help meet those goals. Less than 7% of the 9,304 homes being built citywide are affordable, despite fees on market-rate housing passed in 2016.

Downtown’s growth has been long coming. In 1999, then-Mayor Jerry Brown had a plan that would start to bring 10,000 new residents to the area. But the 2008 recession was devastating, freezing almost all construction in Oakland until around 2015, as soaring rents were pushing both residents and businesses out of San Francisco and eastward.

San Francisco developer Shorenstein Properties first started construction on what would become Blue Shield’s building in the fall of 2008, but suspended work soon after the recession began. The company had already purchased the steel, and ended up storing it in Arizona for nearly a decade.

Tom McDonnell, Shorenstein’s vice president of leasing, sees parallels between Oakland’s transformation and another area that’s seen major changes: San Francisco’s Mid-Market, where Shorenstein bought and renovated what is now Twitter headquarters.

Access to transit and new housing in both areas helped attract new businesses. “When you put such a strong residential component into a commercial area, it changes the vibe of the whole town,” McDonnell said. “There are so many good things going on.”

One thing Oakland doesn’t have is a huge tech sector. Tech accounted for only 3,500 of 65,000 downtown jobs, or about 5%, in the second quarter of 2016, according to a city report. Uber bought the former Sears department store building in 2015 and planned a major new office. But two years later, amid countless corporate scandals, it sold the building. Square has leased it for an expansion office and plans to move in next year.

San Francisco is getting more expensive and it’s increasingly harder to find space, so the likelihood of a big tech push into Oakland is growing, said J.D. Lumpkin, a broker at Cushman & Wakefield.

Rising fees for San Francisco office projects and growth restrictions continue to push rents up. “It’s only going to increase in the coming years. I think that will only be a positive thing for Oakland,” Lumpkin said.

Developers are gearing up to lure big tech. TMG Partners plans to start construction next year on an 875,000-square-foot project called Telegraph Tower that has no tenants. The project’s 15-foot floor heights and three rooftop terraces make it competitive with San Francisco’s new towers, said Lumpkin, who is marketing the property along with Roeder of JLL.

Matt Field, president of TMG Partners, said Oakland has benefited from national shifts toward urban living, and continued challenges around transit and housing make growing in the East Bay more attractive than ever.

“Companies are really trying to get closer to their employees,” he said.

Roland Li is a San Francisco Chronicle staff writer. Email: roland.li@sfchronicle.com Twitter: @rolandlisf