The anti-corruption campaign which has swept across China in the last two years has gone global, as Beijing seeks to enlist the help of western democratic governments in pursuing officials who flee overseas.
Underlining Beijing's rising economic and political clout,Communist party officials have already launched an investigation into assets and individuals based in New Zealand, a country that counts China as its biggest trade partner. It is unclear whether that investigation was conducted inside New Zealand or from China, but investigators have requested permission to interview people in the country.
Read More'Mr. Confession' and his boss drive China's antitrust crusade
In an operation labelled "Fox Hunt 2014", the party's Central Commission for Discipline Inspection,a shadowy organisation with a controversial human rights record, has set up a dedicated office to investigate allegedly corrupt officials who have absconded or sent relatives and assets abroad.
Beijing-based British, US, Canadian and Australian diplomats say they are all under increasing pressure to assist with the Fox Hunt campaign. Hundreds of officials and their associates have taken flight from China amid President Xi Jinping's ever widening anti-corruption campaign.
But the opaque nature of the CCDI and its ambiguous legal status make it very difficult for any western democracy to co-operate.
The amount of money spirited out of China is enormous. The US-based non-profit group Global Financial Integrity estimates illegal flows out of China amounted to $2.83 trillion between 2005 and 2011.
The Financial Times has learnt that the wife, mistress and at least one associate of Cao Jianliao, detained former vice-mayor of the megalopolis Guangzhou, are the subjects of a CCDI investigation.
More from the Financial Times:
Operators in talks to acquire Phones 4U
Valls wins vote and vows to continue reform
Court lifts ban on Uber in Germany
This is despite all of them, as well as Mr Cao's child, being based in New Zealand and at least one of them being a New Zealand citizen.
Mr Cao was detained late last year, and state-controlled media reports have been filled in recent months with lurid tales of his alleged corruption and serial philandering. Mr Cao remains in detention and was unavailable for comment.
The CCDI reports directly to the Communist party and does not answer to courts or police. Although it technically has no legal power to arrest or convict suspects, in practice it can detain party members indefinitely on suspicion of "violating Party discipline".
Read MoreLew warns China on antitrust probes: WSJ
Human rights groups have frequently accused it of torture andinhumane treatment of suspects. Now this extralegal entity appears to be seeking extraterritorial reach beyond China's borders.
New Zealand's Ministry of Foreign Affairs and Trade and the New Zealand Police said they had no knowledge of any CCDI investigation inside the country.
But two people with direct knowledge of the matter said both agencies were aware of the CCDI request and Chinese officials (although not necessarily CCDI officials) had sought access to interview Mr Cao's relatives and associates on New Zealand soil.