The Chinese owner of Oceanwide Center, planned as San Francisco’s second-tallest building, has agreed to sell the property to another Chinese investor for $1 billion.

Oceanwide Holdings said it approved the sale of the partially built property to SPF Capital International Ltd. The deal between the two Beijing companies is one of the biggest real estate transactions in city history. The companies couldn’t immediately be reached for comment.

Oceanwide Center, which started construction in late 2016, calls for a 910-foot tower at 50 First St. that would be second only to nearby Salesforce Tower in height. A 605-foot secondary tower would also be constructed. The project includes 1 million square feet in office space, 265 residential units and a 169-room Waldorf Astoria hotel.

The project is one of the last unfinished pieces of the city’s Transbay district, the high-rise home of tech giants like Salesforce, Google and Facebook, which have snapped up buildings as they have swiftly grown into some of San Francisco’s largest employers, displacing the financial firms that once dominated downtown. It is the largest office project currently under construction in a market with high office rents and little supply.

Only two San Francisco deals come close to Oceanwide’s size: Boston Properties’ $1.22 billion purchase of the four-building Embarcadero Center in 1998, and the roughly $1 billion sale of 555 California St., the former Bank of America headquarters, in 2005 to the Trump Organization, which is a limited partner, and a group of Hong Kong investors, who later sold their majority interest to Vornado Realty Trust.

However, the price tag on Oceanwide Center is unprecedented because the project still requires years of construction to be completed. Oceanwide bought the project land for $296 million in 2015, and completion was previously scheduled for around 2023.

Oceanwide Holdings struggled to finish the project because of the Chinese government’s restrictions on foreign investment, which limit how much money companies can spend in the U.S., said Darlene Chiu Bryant, an executive director of GlobalSF, a nonprofit that works with international investors. She initially connected Oceanwide Holdings to TMG Partners and Northwood Investors, which sold Oceanwide the land.

Oceanwide Holdings officials told Bryant that it had invested $900 million, including the land purchase, in the project to date, she said. Because of rising construction costs, it could take another $1 billion or more to complete the project, she said.

Reuters also reported Wednesday that Oceanwide Holdings’ Han Xiaosheng was no longer CEO, and Wu Chen, formerly deputy CEO, had replaced him. Han will remain executive director and chairman.

The company has never completed a U.S. project. Numerous Chinese developers have struggled in San Francisco amid rising costs and China’s investment restrictions.

SPF Group’s real estate experience isn’t clear. In 2018, SPF Group partnered with China Merchants Group and London’s Centricus to raise $15 billion to invest in tech companies, Reuters reported.

Oceanwide Holdings suspended construction on the shorter tower in October amid rising costs. The San Francisco Business Times reported in November that the building, along with a project in Los Angeles, was for sale.

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