China's attendance at a Vatican conference on combating organ trafficking underlines improving ties between China and the Church and will build momentum for better relations in other areas, a former senior Chinese official said.

Communist China and the Vatican do not have formal diplomatic relations but negotiations towards what would be a breakthrough agreement on the appointment of bishops have made progress, the deputy head of the official Chinese Catholics association said last week.

Chinese academics will join the Vatican conference on Monday and Tuesday, for the second year in a row, state media reported.

'Relations between Beijing and the Vatican authorities are moving forward. So are relations between the two peoples,' Huang Jiefu, a former Chinese vice-minister of health and current head of the National Human Organ Donation and Transplant Committee, was cited in the state-run Global Times as saying.

'The exchanges are beneficial to world peace and are also beneficial to people from the two sides,' said Huang, who attended the conference last year. 'It also creates good momentum to expand contact beyond the health sector to cultural and other areas.'

Last year, the government played down the significance of China's attendance at the conference, saying it probably had nothing to do with two-way ties.

The Global Times said late on Sunday that China would present its efforts to combat organ trafficking and progress on organ donation and transplants at the conference.

For years, organ trafficking was a sensitive issue for China and it repeatedly denied accusations by human rights researchers and scholars that it forcibly took organs from executed prisoners.

In 2015, it banned the systematic use of organs from executed prisoners.

Signs of rapprochement between the Vatican and China have sparked some criticism among Catholic officials in the region.

Cardinal Joseph Zen, the outspoken former bishop of Hong Kong, has said the Vatican was 'selling out' the Catholic Church in China and suggested that there was discord between the pontiff and Vatican diplomats doing groundwork in China.

China refuses to accept the authority of the pope, whom it sees as the head of a foreign state that has no right to meddle in China's affairs.

China's 12 million Catholics are split between 'underground' communities that often recognise the pope and those registered with the state-controlled Catholic Patriotic Association, where bishops are appointed by the government and Chinese Church communities.

But a senior Vatican source told Reuters in February a deal between the two sides on the appointment of bishops could be signed within months.

An agreement would allow the Church to focus on expanding a Catholic presence in a country where Protestant churches are growing quickly.

The Vatican and Beijing have been at loggerheads since the expulsion of foreign missionaries from China after the Communists took power in 1949.

Another source of friction is the Vatican's official ties with self-ruled Taiwan, which Beijing sees as a renegade province.