KiwiRail is coming under pressure to build a link where the new Manukau rail line meets the main trunk at Wiri so passengers can travel south instead of just north as at present.
Mayor Len Brown has promised southern councillors he will do "yeoman's work" to ensure the link is provided sooner rather than later.
Until then, passengers wanting to go south from Manukau on the new line will have to travel north to Puhinui and wait for southbound trains.
Although much of the 2km line has duplicate tracks, they go only north towards Britomart when they link up with the main trunk at Wiri.
That is unacceptable to Papakura councillor Calum Penrose, who says southern residents are in serious need of better public transport to improve job and training opportunities.
Mr Penrose was heartened when Mayor Brown told him and Manurewa councillor Sir John Walker that KiwiRail believed a southern link could be provided for $5-6 million.
However, Mr Penrose feared that estimate might be "a little bit on the light side".
Council safety forum chairman George Wood said it seemed "totally inefficient" to have built the new line without a south-facing connection, requiring people heading that way from Manukau to change trains after travelling little more than 2km.
KiwiRail would not discuss prospects for a southern link or confirm a suggestion that Ports of Auckland's new railhead at Wiri may be in the way.
Infrastructure and engineering general manager Rick van Barneveld said it had not received a proposal from Auckland Transport to build such a link.
Despite the mayor's promise, Auckland Transport spokeswoman Sharon Hunter said no provision for a southern link was being included in a network plan under development by her council-owned organisation.
Mr Wood is also concerned that the new Manukau railway station ends in a trench "in no-man's land", 400m short of the bustling Westfield shopping mall.
Auckland Transport hopes the Manukau Institute of Technology's development of a $94 million multi-storey building above the new station, with a $13.6 million council contribution, will help to boost annual patronage to 600,000 passenger trips.
But rail services are starting modestly, with three trains an hour at peak periods in each direction between Manukau and Britomart, and hourly at other times.
The trips will take about 40 minutes, mainly via Glen Innes on the eastern line, although occasionally through Newmarket.
* 2km from a 300m trench west of the Manukau civic centre to the main trunk link at Wiri.
* Cost: $81 million for first stage followed by $94 million Manukau Institute of Technology building.
* Train services: three an hour in each direction at peak periods; hourly at other times.
* Trip time about 40 minutes.