SINGAPORE, Oct 14 (Reuters) - Rongsheng Petrochemical, the trading arm of Chinese private refiner Zhejiang Petrochemical, has bought at least 5 million barrels of crude for delivery in December and January next year in preparation for starting a new crude unit by year-end, five trade sources said on Wednesday.

Rongsheng bought at least 3.5 million barrels of Upper Zakum crude from the United Arab Emirates and 1.5 million barrels of al-Shaheen crude from Qatar via a tender that closed on Tuesday, the sources said.

The cargoes were likely sold at premiums of more than 50 cents a barrel to Dubai quotes on a delivered basis, one of the sources said.

Rongsheng's purchase helped absorbed some of the unsold supplies from last month as the company did not purchase any spot crude in past two months, the sources said.

Zhejiang Petrochemical plans to start trial runs at one of two new crude distillation units (CDUs) in the second phase of its refinery-petrochemical complex in east China's Zhoushan by the end of this year, a company official told Reuters. Each CDU has a capacity of 200,000 barrels per day (bpd).

Zhejiang Petrochemical started up the first phase of its complex which includes a 400,000-bpd refinery and a 1.2 million tonne-per-year ethylene plant at the end of 2019. (Reporting by Florence Tan and Chen Aizhu, editing by Louise Heavens and Christian Schmollinger)