By David Willey
BBC News, Rome
Not all Chinese Catholics openly practise their religion
The Pope has told Chinese Catholics of the officially tolerated Patriotic Church and those who worship secretly to take steps towards reconciliation.
Beijing broke off formal diplomatic relations with the Vatican in 1951, and Catholic worship is only permitted in officially recognised churches.
But members of the underground church have kept their allegiance to Rome.
It is estimated that, altogether, there are more than 10m Catholics throughout China.
Pope Benedict XVI's message took the form of some footnotes and additions to a letter that he originally sent two years ago.
In that letter, he praised members of the so-called underground church who have remained faithful to Rome during more than half a century of communist rule.
While recognising the Pope as their spiritual leader, the officially-sanctioned Patriotic Church appoints its own bishops and priests without reference to Rome.
Millions of Chinese Catholics - no-one knows exactly how many - still worship in secret or semi-secret in unofficial Catholic communities.
From time to time they are subjected to harassment and persecution by the authorities.
The Vatican recently denounced a new wave of arrests of underground priests and bishops.
High level negotiations have been going on during the past year between Vatican officials and Beijing with a view to restoring diplomatic relations. But progress has been slow.
The latest message from the Vatican published on a new Chinese language Vatican website encourages the faithful in China to get together at grass roots level with their fellow Christians and to settle their differences in the interests of church unity.
The Pope regards the eventual reunification of both Patriotic and underground Chinese Catholics as one of his most important priorities.