Buses will replace trains at Auckland's southernmost station after it was hit by a major signal fault this morning, the second delay for Auckland commuters in as many days.

Auckland Transport (AT) is apologising to commuters, saying all train services to and from Pukekohe would be affected.

The fault happened the same week Auckland's uni students head back to study, traditionally a time of mayhem and major delays on the roads and commuter lines.

AT says today's fault is isolated to the Pukekohe station, on the network's southern line.


Spokesman Mark Hannan said speculation on social media that the train station's building had been closed or condemned because of structural damage was untrue.

The signal box at the station had a possible crack in it and engineers were checking it, he said.

Yesterday afternoon commuters faced delays because of a broken rail in Britomart's train tunnel.

Fewer carriages operated for several hours on the eastern line and the service to Onehunga was cancelled, causing crowding and delays.

Gulf Harbour ferry services have also been replaced by buses this morning.

Auckland Transport said bad weather has forced the cancellation of ferry sailings from the Whangaparaoa marina to downtown Auckland.

University students returned to study this week, but the usual March madness on Auckland's roads was a little less crazy this year, thanks in part to more people using trains.

March traditionally has 8.5 million passenger trips across the public transport network, 30 per cent more than in February and April.

Last year the annual traffic nightmare led to more than 1100 Auckland bus complaints made in submissions to Generation Zero as part of its Better Bus campaign.

Queues of up to 40 people waited for as long as 1.5 hours for buses in some parts of Auckland last year, but extra services this year helped ease congestion on Monday.

Traffic congestion usually takes a breather in April as students' timetables settle and workers take breaks during the Easter holidays.