A spokesperson for Auckland Transport said that standing on a train is "part of living in a big city".

"There are services that are very busy at the moment," a spokesperson told Newshub.

"It's perfectly safe for people to be standing on a train."

Rail and Maritime Transport Union organiser John Kerr says the strike is about safety.

"Auckland Transport and Transdev want to take train managers off the trains and our members are saying that's going to compromise public safety and they're not prepared to do that.

"[Train managers] are first responders in the event of an emergency, they do crowd management and they're also operational, so if there's a signals failure they intervene. They're really a critical member of staff."

Auckland Transport says it is proposing to transfer the responsibility for train door opening and closing from train managers to train drivers with specific safety controls, pending safety case approval from independent rail regulator, NZ Transport Agency.

Train managers will be replaced with a larger team of roving transport officers who will be trained to manage anti-social behaviour and have flexibility to move around.

Auckland Transport and rail operator Transdev say they have developed a temporary timetable to minimise disruption and provide consistent rail services on these lines during the next three weeks.