New World Development aims to sell the remaining 11 floors at Grand Millennium Plaza in Sheung Wan at an average price of HK$5,000 per square foot, according to director Stewart Leung Chi-kin.
The developer last month sold the low block of the office project to the Government of Singapore Investment Corp for HK$1.38 billion.
If the high block's remaining floors were sold, New World could cash in another HK$1 billion.
However, Mr Leung said New World did not need to hasten sale of the high-block floors after the sale of the low block, the largest office investment transaction since 1997.
He said the remaining floors at the high block, now named Cosco Tower, spread over the high and low zones of the building.
The 55-storey tower has about 850,000 sq ft of floor area, each floor about 20,000 sq ft.
The top 15 floors were sold to the mainland-funded Cosco Group for HK$3 billion, or HK$10,000 per square foot, several years ago.