Police investigating the runaway couple with $3.8 million of Westpac's money believe they have fled to Hong Kong.
Interpol are leading a search in Hong Kong through official channels in Beijing to try and locate the pair, thought to be "Leo" Gao and girlfriend Kara (or Cara) Young.
Detective Senior Sergeant Harvey of Rotorua CIB said officers were working with the family of one of the couple, who were shocked at their name being associated with the case.
Westpac, who have not publicly identified the account holder, said today the customer in question (Gao) had in place a temporary overdraft facility with a limit up to $100,000.
"It sought to formalise that limit, at which stage an error occurred, the consequence of which was opening up that limit to $10 million."
The customer then attempted to transfer amounts totalling around $6.7m, but the bank has managed to recover $2.8m.
"Westpac is continuing to vigorously pursue the outstanding amount of $3.8m," the bank said.
Records list Mr Gao, along with Huan Di Zhang, as the owners of the service station known as BP Barnetts. It was placed in receivership this month.
The money was believed to be in the account on or about May 5 but it was only on Wednesday this week that police publicly said they were investigating.
Westpac said the blunder was put down to human error and did not directly involve its Rotorua branch.
It said it had "taken and continue to take all necessary steps to prevent a mistake such as this happening again".
The whereabouts of Mr Zhang, who owns 60 per cent of the BP Barnetts business, is unknown.
The money was in the account on or about May 5. The following day, the BP station closed its doors. But it was only on Thursday this week that police said they were investigating.
In the meantime, Westpac hired a private investigator - Mike Dingwall, who describes himself on his business card as a "former police licensed investigator" - to conduct inquiries.
Senior Sergeant Harvey said police had called on Interpol to help find "individuals associated with the account" who were believed to have fled the country with a large sum of money "mistakenly advanced" by Westpac.
Police refused to answer questions yesterday and released only scant information.
However, a neighbour said she understood Ms Young was with her mother in Blenheim and had not fled NZ.
Chevi Lambert, manager of Andy's Cellar close to the BP, said Gao phoned his girlfriend and told her to get out of town.
"I don't know when the money went out into his account, but I know he did a runner on the Wednesday."
Ms Lambert said Mr Dingwall had visited her shop with a photo of Ms Young, asking if staff recognised her.
"And our answer was, 'Yes, it's Leo's girlfriend'."
Mr Dingwall told staff he had proof Gao had left the country and that records showed Ms Young had used his credit card in Auckland on Wednesday, May 6.
"That's the reason they thought she was involved ... because she had tried to use Leo's credit card."
One report last night suggested a police liaison officer had been sent to China to search for the missing millions and those behind its disappearance.
Tania Davis, director of ZeroTo100Automotive which adjoins the BP, knew the business was in real strife when she saw a receivership notice left at the station.
Banking Ombudsman Liz Brown said that it was generally a criminal offence for people to spend money accidentally put into their account if they knew it wasn't theirs. In her 15 years in the role she had been involved in 10 to 20 cases of this nature.