CHINA has set 1995 as the target year to eradicate polio but its efforts have been hampered by the country's large size and an increasingly mobile population, an official said yesterday. After a cheque presentation ceremony in Hong Kong yesterday, Guo Xianzhi, a deputy director of the Ministry of Foreign Trade and Economic Co-operation, said another problem was insufficient vaccine production capacity. ''The Chinese Government is making every effort to achieve the eradication of polio by the year 1995 . . .. That's the guarantee made by the Chinese Government not only to children in China but also to children of the world,'' said Mr Guo. The Ministry of Public Health estimated China would need about $530 million to eradicate polio. As much as $460 million will be used to purchase vaccine. Mr Guo said although impressive results had been achieved in the fight against polio, the next two years would be critical. ''From several thousand cases down to 1,000 cases is a little easier. However, for the last few hundreds, if you consider China's large area and population . . . it could be no easy job,'' Mr Guo explained. China has reported a steady decline in polio in the past three years. In 1990 it registered over 5,000 cases of polio and the figure dropped to 1,191 last year. However, it is believed cases of polio could be many times higher than those reported. Under the present plan a nationwide polio eradication campaign will be launched in early December, when every child under the age of four will be given one pill of vaccine. A second pill is to be administered early next spring. ''At the moment we have about 100 million children who are under four years old, so you can imagine the efforts, the cost and resources involved in this are very immense,'' Mr Guo said. In addition, the Government also needs to provide vaccine for the 20 million newborn babies each year. By 1989 China had received over $150 million from the United Nations to improve its vaccine storage facilities.