Two trains breaking down at the same Auckland station at the start of the day caused yesterday's commuter chaos.
Auckland Transport says the breakdowns at Papakura at 6.30am yesterday blocked the main trunk line and there were difficulties moving one of the diesel trains.
It took two hours for services through Papakura to resume, and the knock-on effect was delayed services for much of the day.
The double breakdown is the latest of more than 200 cancellations and delays this month because of faults in the ageing diesel fleet.
"The last couple of months has seen and increase in diesel mechanical issues," said Auckland Transport general manager of public transport Mark Lambert.
Mr Lambert said the high number of disruptions was partly also a consequence of moving to a higher frequency of services, meaning one breakdown affected a larger number of following trains.
The fleet is being progressively replaced by new electric trains.
Auckland's smaller Eastern, Onehunga and Manukau lines are now fully electric, with electric trains beginning to run on the southern and line, and both the southern and western due to go fully electric in July.
The diesel powered trains and locomotives are maintained by Kiwirail for the operator TransDev.