INTERNATIONAL companies Coles Myer, Sansui and Chemihan, have signed leases totalling 17,000 square feet for office space in China Hongkong City in Tsim Sha Tsui. The buying office for Australian retail chain Coles Myer will take 5,000 sq ft, while electronic companies Sansui and Chemihan are to lease 7,000 sq ft and 5,800 sq ft respectively. Agents Richard Ellis reported a healthy start to this year, with a high number of leases already committed. Spokesman Mr Adam Blazeby said the operation was progressing smoothly. As agent for Sony Semiconductors, Chemihan had specific requirements which Richard Ellis had been able to meet, Mr Blazeby added. ''The tenants have been able to take over fully fitted premises, making considerable savings on fitting out costs,'' he said. ''The availability of suitable accommodation is becoming more restricted. ''Vacancy rates for Grade A space is around four per cent in Tsim Sha Tsui and close to two per cent in Canton Road, as Harbour City nears full occupancy.'' The prospect of falling vacancies and increased activity is expected to result in rental increases this year. New space of any considerable size - apart from the Park Lane Square II development on Nathan Road - will be scarce. Mr Richard Watton, associate director of Richard Ellis Kowloon said he expected rentals to rise between 20 and 25 per cent during 1993. ''This will happen as the market reacts to the relatively limited supply,'' he said. ''There is very little decentralised accommodation available to lease this year, with the majority of supply for sale. This puts further pressure on prime rental accommodation.''