SEOUL (Reuters) - Chinese planemaker COMAC opened in Hong Kong its second office this week outside mainland China, a subsidiary said on Thursday, as the state-owned company tries to break into a global passenger jet market dominated by Western manufacturers.

COMAC's two commercial passenger planes are, with the exception of one Indonesian airline, all flown within China, but the firm is seeking to expand overseas at a time when market leaders Airbus and Boeing ( BA ) are struggling to make planes fast enough to meet demand.

The launch of the COMAC Customer Service Hong Kong Office follows the opening in Singapore on Monday of COMAC's Asia-Pacific office, billed as a way to expand the planemaker's reach overseas.

Li Ling, COMAC deputy general manager, said the Hong Kong office was an important step in the planemaker's international strategy, the statement from COMAC's customer service arm Shanghai Aircraft Customer Service Co said. 

"COMAC looks forward to working hand in hand with all parties to strengthen exchanges with the aviation industry in Hong Kong and even Southeast Asia with a more open attitude," Li said.     

Hong Kong is a special administrative region of China with its own civil aviation regulator. No COMAC planes currently fly to the city or have been ordered by Hong Kong-based airlines, although there have been two demonstration flights of COMAC's C919 jet in Hong Kong over the past year.

On Wednesday, COMAC also signed a memorandum of understanding to expand business with Hong Kong-based aircraft maintenance group HAECO to collaborate on airframe, engine and component services.

HAECO is owned by Hong Kong conglomerate Swire Pacific ( SWRAF ), the biggest shareholder in Cathay Pacific Airways.

"The MOU will enable the two parties to jointly deliver more comprehensive support towards COMAC's domestic and international customers," said a statement from HAECO, which already works with COMAC in mainland China. 

COMAC has stepped up plans for production and sales of its C919 narrow-body passenger plane, which competes with Boeing's ( BA ) 737 MAX and Airbus' A320neo jet families. The Chinese company also has plans for larger, wide-body designs.

Industry sources say COMAC is a long way from making inroads internationally, especially without benchmark certifications from the European Union, which it is pursuing for the C919, or the United States.

COMAC previously opened a U.S. overseas office in 2010 in California, and a European office in Paris in 2011 during earlier pushes for international certification and cooperation.

Their current status is unclear.