A cracked rail between Town Hall and Wynyard station is causing major delays across the Sydney rail network this morning.

The city circle line was closed in one direction towards Wynyard earlier today as urgent rail repairs took place, causing disruptions for morning commuters.

City Rail says the crack has been repaired and services are now running in both directions around the city circle.

Commuters should expect delays though, as the rail team works towards clearing the backlog of services that have built up.

Affected lines are T1, T2, T3, T4, T8. The T8 twitter account posted this message at 6.40am: “ ... any customers delayed getting to a flight due to this disruption please make yourself known to staff or contact 131500.”