By Trixie Yap, Chen Aizhu and Siyi Liu

SINGAPORE, March 3 (Reuters) - Zhejiang Petrochemical Corp, a major Chinese refiner backed by Saudi Aramco, is shutting a 200,000 barrel per day crude unit for overhaul in March, cutting throughput by 20% from February, the company told Reuters on Tuesday.

The month-long shutdown comes as global oil supplies tighten and prices surge due to the widening conflict in the Middle East.

"We had earlier planned the overhaul around March and April, and now we're bringing this forward under the current circumstances," a company official said.

Privately-controlled ZPC has a 20-year supply agreement with state-run Saudi Aramco 2222.SE for 480,000 bpd of crude and operates four 200,000-bpd crude units in Zhoushan in eastern China, making it one the country's biggest refiners.

Aramco owns a 10% in Rongsheng Petrochemical 002493.SZ, ZPC's largest stakeholder.