A source told the Rotorua Review newspaper a police liaison officer was sent to China recently to search for the couple.
Neighbouring business Zero to 100 Automotive director Tania Davis says the BP was owned by an Asian man nicknamed "Leo" who had a New Zealand girlfriend.
She says on May 7 the business was open, but the next day it was closed and a notice was left saying it was in receivership.
"Deliveries arrived and just piled up outside the front door. A few people started to help themselves to some newspapers and supplies that were there," Ms Davis said.
She says BP staff arrived yesterday and took away the remaining fuel and tanks. The shop is now empty.
Detective Senior Sergeant David Harvey held a media conference in Rotorua this afternoon, but would not confirm any speculation. When asked where police believed the money had gone, he simply replied "overseas", before refusing to answer any further questions.
A Westpac spokesman today refused to confirm the amount mistakenly given to the couple, though said the bank was "pursuing vigorous criminal and civil action to recover the sum of money stolen".
He said human error was responsible for the couple's substantial windfall, not a systems error, and that the bank was reviewing its procedures.
Detective Senior Sergeant Harvey was prepared only to say that an investigation had been launched into a substantial sum of money that had been "mistakenly advanced" from Westpac.
View Larger Map
Police had received a complaint from Westpac relating to people living in Rotorua.
He refused to say how much money was involved.
Police were investigating because the Westpac bank considered what had happened was theft or fraud, through the use of a document to obtain a pecuniary advantage, Mr Harvey told Rotorua's Daily Post newspaper.
He confirmed some of the money mistakenly advanced had been withdrawn from the bank account but was not prepared to say how much money was involved.
He expected the investigation to "take some time".
Banking Ombudsman Liz Brown told the Daily Post that generally speaking it was a criminal offence for someone to spend money accidentally put into their bank account if they knew the money wasn't theirs.
In her 15 years as banking ombudsman she had been involved in 10 to 20 cases of this nature. They were legally referred to as "payment by mistake".
She was unable to recall how much money was involved in each case.
"There haven't been cases of millions of dollars but certainly ones where there have been several thousand dollars," she said.
Massey University banking lecturer Claire Matthews said the lucky recipients would probably not get away with it.
"They've taken funds that they're not entitled to, that are not theirs," she told Newstalk ZB.
"They've effectively, I guess, become thieves but it is only going to be a matter of time."
The business owners would be hard pressed to argue they honestly believed they were entitled to such a huge sum of money, she said.
Westpac said this morning court action had begun to recover the money but refused to comment further.
- NZPA, NEWSTALK ZB, NZ HERALD STAFF