Sydney rail commuters will be eligible for refunds for avoidable train delays of 30 minutes or more under a policy Labor has promised to introduce if it wins the state election in March.

The election promise came as Sydney commuters endured significant delays to train journeys during the morning peak on Monday after more than 110 staff called in sick.

And disruptions continued into the evening peak after Sydney Trains cancelled a number of services on lines such as T1 Western, Northern and North Shore, and the T2 Inner West. The cancellations were expected to be fewer than the 57 on Monday morning.

By 6pm, frustrated commuters facing severe overcrowding, delays and cancelled services had returned to Twitter to vent.