'It is really hard to say because registering a drug costs a lot of money and it depends whether they think this market is profitable,' Mr Hao said on the sidelines of the launch of a programme to provide Aids education to migrant workers.

He said if the drugs were made available in China, the government could use donations from the United Nations' Global Fund to Fight Aids, Tuberculosis and Malaria to provide free second-line antiretrovirals to patients who were resistant to first-line drugs.

The government is providing free first-line drugs to rural Aids patients and those in urban areas facing financial difficulties, but second-line drugs are not yet available in the country.

Drug resistance has emerged among many patients and there are rising calls for Beijing to provide second-line drugs - which are a lot more expensive - to patients who are in need.

Mr Hao estimated there were about 4,000 to 5,000 Aids patients who needed to shift to second-line drugs based on the international average that about 20 per cent of the patients who had been infected with the virus for several years would develop resistance.

Henk Bekedam, the WHO's China representative, said earlier that Aids patients from poor countries would not be able to afford antiviral drugs in five years if prices did not fall.

The central government has joined with the International Labour Organisation and the US government to launch an Aids education programme for migrant workers in Anhui , Guangdong and Yunnan .

Mr Hao said a survey showed only 20 per cent of migrant workers had some understanding of Aids.