Extra taxis and train carriages will be pressed into service in Auckland this morning to try to cope with the start of an unprecedented six-day strike against the region's main bus fleet.

The Auckland Regional Transport Authority was also working overtime yesterday, negotiating replacement services from bus operators not hit by the Stagecoach pay dispute, although these will not be enough to save tens of thousands of passengers from being stranded.

"Everything will be full on tomorrow," said a supervisor at the Howick and Eastern bus company, which has been asked to pick up passengers on request on what are usually non-stop services from eastern suburbs to Auckland.

Other companies will provide skeleton services in other parts of Auckland.

Transport authority chief executive Alan Thompson admitted limitations in the availability of non-Stagecoach buses and drivers, who have been given union approval to fill gaps left by the strike.

Mr Thompson said: "We are doing what we can with what we've got."

This also includes providing extra train carriages.

But he expressed deep concern at the overall impact of the strike on the credibility of public transport, both over the six days and in the long term.

"We continue to be concerned at the inconvenience ongoing strike action is causing bus users and the long-term effect that this could have on bus patronage."

Taxis are preparing for a roaring trade as well, although Auckland Co-operative Taxi Society spokesman Gene Julian expects extra traffic congestion and customer demand to make it harder for everyone to get where they want.

Stagecoach expects to lose almost 700,000 passenger trips during the six days of the strike by about 1000 drivers from four unions.

This will affect 70,000 to 75,000 passengers on each of four weekdays of the strike, of whom more than 25,000 will be schoolchildren or tertiary education students, and who on average take 2.1 bus trips a day.

Auckland University Students Association president Greg Langton expects many of his members will be forced to stay at home today and tomorrow, and on Monday and Tuesday next week.

About 30,000 Aucklanders rely on Stagecoach buses each day to get to work, leading to a plea by the Northern Employers and Manufacturers Association for flexibility from both firms and their staff.

Chief executive Alasdair Thompson said that if people were genuinely unable to get to work, they should offer to take the day off, either without pay or to use their leave.

"If people take sick days off, it just stands out a mile - they shouldn't expect flexibility just on the part of employers."

The head of Transit New Zealand's traffic management centre at Northcote, Simon Gough, said a one-day strike by Stagecoach drivers last month did not appear to upset motorway flows.

But he suspected this might have been because some people chose to stay at home, and he feared the impact of a far longer strike threatening the region.

Stagecoach late yesterday made a renewed call to the bus unions to call off the strike, saying it would be pointless and would reduce the amount of money left to the company to settle the pay dispute.

Executive chairman Ross Martin said the strike was in defiance of an Employment Relations Authority recommendation that the drivers accept an offer amounting to a 14.8 per cent wage rise over three years, plus $600 in cash.

He said the company would make an application today for a binding pay determination from the authority, although he ruled out seeking any injunction to stop the strike.

Another Stagecoach spokesman, Russell Turnbull, confirmed the company would not try to operate any of its buses through picket lines now that the most moderate of four unions had confirmed its intention to support the strike. But he said about 100 or so non-union drivers would be expected to report to work, even if only for bus-cleaning duties.

Combined unions advocate Gary Froggatt doubted the company would succeed in gaining a binding ruling from the authority, saying it would have to prove a serious breach of good faith by the drivers.

He denied they were guilty of such conduct, but said: "We have plenty of evidence of bad faith on the company's part."

Asked what last-minute message he had for passengers stranded by the strike, he said they should urge the company to provide its drivers "with decent wages and conditions".

Mr Froggatt said there would be pickets this morning at all eight of the company's depots.