Following the raid, Mr Yan, dressed casually in a black tracksuit, met defence lawyer Simon Lance in the Metropolis lobby.
No criminal charges have been laid. Mr Lance would not comment on what the police had taken. "However, Mr Yan does deny any alleged money laundering or other illegal activity. He has not been arrested."
The police would not answer specific questions, but released a statement from Detective Senior Sergeant Craig Hamilton, the officer in charge of the asset-recovery unit.
"Police have begun the process of restraining the assets of a 43-year-old Auckland businessman and his 38-year-old female partner as part of an ongoing Criminal Proceeds Recovery investigation," it read.
"This is a complex investigation which is focused on the laundering of large amounts of money that police believe has been accumulated through illegal activity.
"Police are working hard to ensure that innocent third parties who are involved in business arrangements with the couple will have their interests protected and that only those directly involved in money laundering activities will be affected by the restraint of assets."
The Criminal Proceeds Recovery law essentially forces someone to prove how an asset was paid for - even if they were acquitted or criminal charges are not laid.
Inquiries by the Weekend Herald have discovered the Metropolis raid stems from an ongoing financial investigation into a friend of Mr Yan, Yingzi Zeng, from whom $9 million in assets were seized in December.
Her assets, frozen by a High Court judge, included a late-model Porsche and Maserati, a $3.9 million lifestyle block, an apartment, a large home, bank accounts and businesses.
The court order was made alongside six others affecting people who face charges of importing and supplying the class-B drug pseudoephedrine following the record-breaking Operation Ghost investigation.
Hundreds of charges have been laid against more than 38 people in an inquiry where nearly 600kg of drugs have been seized. But no charges have been laid against Ms Zeng, who lives in East Auckland.
Mr Yan stood trial in the High Court at Auckland in May 2012 after pleading not guilty to five charges relating to false declarations on immigration and citizenship papers. Justice Timothy Brewer found him not guilty despite saying the evidence put before him "proves a situation that is highly suspicious".
Most of the documents were false but were filled out by others on Mr Yan's behalf. "In the absence of firm evidence that the accused knew of the falsity ... there would need to be proof of dishonest intention in using the Liu Yang identity," the judge said.
Mr Yan has been a permanent resident in NZ since 2002. In 2005, he applied for citizenship, but this was opposed by the Internal Affairs because his true identity was not known.
He was then granted citizenship by minister Shane Jones against the advice of officials. His citizenship was conferred in a VIP ceremony in Wellington after lobbying from Dover Samuels, a Labour MP at the time, who regards him as a close friend.
Last year, the Auditor-General investigated how Mr Yan came to be granted citizenship, but found no evidence of any wrongdoing.
William Yan
2001: Arrives in New Zealand with two identities, Yang Liu and Yong Ming Yan.
2002: Granted permanent residency as Yang Liu.
2005: Applied for citizenship. Makes donations to Labour and National.
2007: Immigration New Zealand's moves to revoke permanent residency vetoed by minister.
2008: Three MPs write in support of citizenship application. Citizenship approved by ministerial prerogative, against advice of officials. Ceremony held at Parliament. Changed his name to William Yan.
2009: Arrested at Auckland Airport and charged with making false declarations on his immigration and citizenship papers.
2012: Found not guilty in High Court at Auckland, despite Justice Timothy Brewer saying the evidence put before him "proves a situation that is highly suspicious".
2013: Auditor-General releases report which criticises former Cabinet minister Shane Jones for granting citizenship but said there was no evidence of wrongdoing.
Thursday: Police raid Mr Yan's penthouse and seize his assets.
