The bank that mistakenly handed a New Zealand couple a $6.1 million credit limit said Friday it had recovered less than a third of the money from the pair, who have disappeared.

An international police search is under way for the couple, who are believed to have gone on the run to avoid having to give the money back.

Police have not identified the couple. Detective Senior Sgt. David Harvey said Interpol was investigating in Hong Kong and was also working with officials in Beijing.

Westpac Bank on Friday offered more details of its mistake.

The bank said in a statement that the couple, who ran a gas station in the city of Rotorua, had a bank overdraft of New Zealand $61,000. Westpac had said on Thursday that the couple's overdraft was worth NZ$10,000.

The bank "sought to formalize that limit, at which stage an error occurred, the consequence of which was opening up that limit to" $6.1 million, the statement said.

The account holder had tried to transfer about $4 million out of the account, but the bank had been able recover $1.7 million of it. The statement did not specify just how it got the money back.

"Westpac is continuing to vigorously pursue the outstanding amount," of $2.3 million, the bank said.

Westpac says it considers the money to have been stolen but conceded it was human error at the bank that made the couple accidental millionaires.