Two new Transbay towers will further transform San Francisco’s skyline: a 910-foot building that will be the city’s second-tallest and a 605-foot spire alongside it.

With 265 residential units, a 169-room Waldorf Astoria hotel and 1 million square feet of new offices, the complex called Oceanwide Center will have more floor space than Salesforce Tower.

But Chinese developer Oceanwide Holdings needs more cash to complete the towers, according to four people with knowledge of the project. Oceanwide is seeking additional construction financing, and a deal could close in the next few months, said the sources, who weren’t authorized to speak publicly. The amount and source of funding isn’t clear.

The city’s ongoing boom, with San Francisco and Silicon Valley companies competing for space and talent in tech’s new heartland, will likely bolster the project. Still, Oceanwide Center is the only major office project under construction in San Francisco that doesn’t have a tenant, though some tech companies are interested.

Salesforce, the city’s biggest private tenant, is considering a lease for all 1 million square feet of office space, or room for more than 6,000 employees, according to two people familiar with the company’s discussions. A deal — which could be the biggest lease in city history — has not been signed. Salesforce — which also leases about two-thirds of the Salesforce Tower — declined to comment.

Amy Jalili, an Oceanwide spokeswoman, said it is “committed to completing the project,” and targeting an opening in 2022. She declined to comment on financing or leasing activity. Construction started in late 2016 and is ongoing.

Oceanwide, a Beijing conglomerate with $2.4 billion in 2017 revenue, is facing challenges with another large project. In January, it stalled construction on its $1 billion Oceanwide Plaza project in downtown Los Angeles as it sought to “restructure capital,” according to the Los Angeles Times. Construction restarted in March. Oceanwide is also selling a New York building after owning it for three years, according to the Commercial Observer.

Oceanwide is seeking more money in a more difficult environment for Chinese investors in the U.S.

Chinese foreign direct investment in the U.S. plunged from $29 billion in 2017 to $4.8 billion last year, according to research firm the Rhodium Group. The drop followed capital restrictions by the Chinese government. The Trump administration has also raised tariffs on Chinese goods and sought to block some Chinese investments in the U.S., such as a 2017 bid for San Jose company Lattice Semiconductor. However, Oceanwide received U.S. approval to take over Virginia insurance firm Genworth Financial.

Other Chinese developers such as Z&L Properties have faced project delays and lawsuits amid the financial restrictions and the Bay Area’s complex land use and construction regulations.

Oceanwide has already invested hundreds of millions of dollars in the San Francisco project. In 2015, the developer paid $296 million for the Oceanwide Center site at 50 First St., part of a wave in Chinese investment in the Bay Area and around the country. Oceanwide will also pay $130 million in city fees for community benefits like transportation improvements, The Chronicle previously reported.

Developer Boston Properties, which owns nearby Salesforce Tower, has said Oceanwide Center is drawing interest from other parties.

“The project has got some, I think, some timing issues. Lots of people are trying to understand how they might be helpful in that situation,” Owen Thomas, CEO of Boston Properties, said on an earnings call last week. He declined to answer questions on the call about whether Boston Properties is seeking involvement in Oceanwide Center.

Oceanwide Center is poised to benefit from San Francisco’s tight office market, which has a vacancy rate under 6%. But future office projects in central South of Market are grappling with multiple lawsuits against recent legislation that raised building heights there. The city’s 1986 Proposition M caps the amount of office space that can be approved each year.

The dearth of space and continued demand from the tech industry has led to leases for future buildings that haven’t even been approved by the city, such as Salesforce’s lease at 564 Howard St. and Pinterest’s deal at 88 Bluxome St.

“The vacancy rate is at its lowest level since this last cycle began after the great financial crisis. You will be hard-pressed to find an existing 100,000-square-foot block of continuous space in the market direct or sublease,” Thomas said on the Boston Properties earnings call.

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