Three years after being rescued from extinction, the Overlander passenger trains are to have their services between Auckland and Wellington boosted.

KiwiRail has announced daily services for most of the July school holidays, instead of just three days a week, and an extension of its peak season to more than seven months of each year.

That follows a 25.5 per cent increase in patronage over the past year - a far cry from 2006 when former rail operator Toll threatened to axe the trains after failing to obtain government subsidies to make up for sluggish demand.

The company relented after a rescue campaign by councils along the route, headed by Auckland regional chairman Mike Lee, who offered his organisation's assistance in promoting what international travel writers have acknowledged as one of the world's classic scenic rail journeys.

But it trimmed the operation to just three services a week in each direction for much of the year, while offering to run a daily service from December to May - but only if patronage picked up.

The Overlander trains have since been renationalised as part of the Labour Government's purchase of KiwiRail, which has reported a steady increase in passenger numbers.

That prompted a decision by KiwiRail subsidiary Tranz Scenic to run the trains every day from July 6 to July 19 for the winter school holidays and then from September 25 until May next year.

"This represents a great success for a train service which, only a few years ago, was in jeopardy," said KiwiRail passenger general manager Ross Hayward.

"We have been seeing steadily increasing passenger numbers, building over the last 18 months."

Tranz Scenic spokesman Nigel Parry said yesterday although the trains had a normal capacity of 160 seats, extra carriages were sometimes added to cater for growing demand.

That had helped boost passenger numbers by 25.5 per cent for the 11 months to May, compared with the same period of the previous year.

Mr Parry said the achievement was particularly pleasing in tough times.

Ruapehu District Council member and National Park resident Murray Wilson welcomed the service increase as a vote of confidence in the longevity of the trains, but looked forward to the restoration of year-round trips.

"We are pleased and we do understand them reducing services during the winter, but for the long term, they need to operate seven days a week and be promoted to the world," he said.

Mr Lee, who led a delegation of council leaders on an Overlander trip to Wellington to persuade Toll to spare the trains, said the latest announcement was "marvellous".

"It just proves that if you provide the facility and you promote it, people will use rail," he said.

"We pledged to back it, in terms of helping to get bums on seats, and to [Toll chief executive] David Jackson's great credit, they changed their mind and kept it on, but they were within a couple of weeks of knocking the thing right off."