HANOI, Jan 5 (Reuters) -

Output from Vietnam's largest oil refinery is expected to fall by 20%-25% during the first 10 days of January as its residual fluid catalytic cracking (RFCC) unit has been shut down due to a technical problem, the government said on Thursday.

The 200,000-barrel-per-day Nghi Son Refinery and Petrochemical has a leak at the RFCC unit, the government said in a statement.

Reuters first reported on the shutdown late last month.

The Ministry of Industry and Trade has asked fuel traders to increase their imports to compensate for the shortfall "to ensure sufficient fuels for the local market until the end of the first quarter," the government said.

As a result, Petrolimex has issued tenders since Dec. 30 to buy at least three cargoes of 500 ppm sulphur gasoil for January to February arrival to cover this shortage in the local market, several trading sources said.

Nghi Son refinery is 35.1% owned by Japan's Idemitsu Kosan Co, 35.1% by Kuwait Petroleum, 25.1% by Vietnam's state oil firm PetroVietnam and 4.7% by Mitsui Chemicals Inc. (Reporting by Khanh Vu; Editing by Barbara Lewis and Nivedita Bhattacharjee)