The desktop in question was in the Christchurch offices of Westpac, a leading New Zealand bank. At its keyboard sat a woman with 30 years' experience who was about to perform a routine task: formalising an overdraft facility. The account was that of Mr Leo Gao, 29, who ran a filling station in Rotorua, a tourist town on North Island.

The bank had agreed to give the couple a $100,000 (£39,000) lifeline, and the woman was entering the amount on a loan clearance form.

Every digit, including the two zeroes for the cents, was put in. But one thing wasn't: the decimal point. And its absence gave Gao and his partner Kara not $100,000, but one hundred times that amount. Suddenly, the couple, who had been heading towards insolvency, had $10m, and a lot of temptation, in the bank.

Westpac did not at first spot the error – a supervisor missed it – but soon after the money was transferred on Monday 5 May, Gao did notice. But then, to a man used to seeing the letters OD all over his bank statements, the sudden replacement of them with a bottom-line credit in eight figures would rather catch the eye. If he was fleetingly inclined to call the bank and tell them of their mistake, the feeling soon passed. Instead, he began to make hasty plans to take the money and run.

He and Kara told friends they were about to go "on holiday"; and, unlike other couples who have hit the road after similarly accidental windfalls, they invited the family to join them. Several de­clined, but Gao's mother, and her sister, Aroha Hurring, agreed to drop everything and come along for the ride.

Kara's seven-year-old daughter Leena, naturally came too, and Gao's business partner, Huan Di Zhang, also decided to do a flit. That decimal point was changing quite a few lives.

To say they left in a hurry is something of an understatement. Gao and Kara closed the petrol station (bequeathing a shock to the few regular customers, and its sole employee, Shybu Antony); left Sam, their border collie, tied up by the kennel in the backyard of their three-bedroom home; and headed for Auckland, three hours' drive away.

There was no time to clean out their car and when the white Holden Commodore utility vehicle was found at Auckland Airport, sitting forlornly in Row B of the long-term car park, the back seats were covered in a dirty duvet, a bag of Pedigree dog biscuits, and rusty handsaw. The windscreen displayed a Warrant of Fitness that expired three months ago.

They were ticketed through to Hong Kong, and had landed and cleared the usual channels before Westpac realised their error. By 7 May, Gao and party were thousands of miles away from New Zealand police, on the territory of other jurisdictions altogether, and now in with a serious chance of getting away with it.

Maybe it was the euphoria, but they didn't fancy a period of restraint, anonymity and self-control. They moved on to Macau, and started spending like there was no tomorrow, which, in their case, was a plausible assumption. There were reports that they'd hit the local casinos, and Westpac, which seems to know more than it has so far div­ulged, last week named Wynn Resorts, which owns a Macau casino, in a lawsuit seeking to recover the lost millions.

Westpac hired a private detective, Mike Dingwall, and the first that some of Gao's connections knew of what he'd done was when Dingwall turned up on their doorstep, brandishing photographs of the absconders, and asking questions. Few people had any significant answers.

Probably even more frustrating for the bank is the continued absence of their money. Of the NZ$10m (£3.9m) overdraft, Gao tried to transfer $6.7m, $2.9m of which was swiftly recovered, leaving him with $3.8m (£1.48m).

With his nationality, appearance and mother in tow, finding him among China's population of 1,330,044,544 will be something of a challenge; especially as the Chinese police are not, more than three weeks after he absconded, formally looking for him. Interpol, not noted for its strong presence in Beijing, is said to be involved, and an New Zealand officer has reportedly flown there to try to find the couple.