SYDNEY - Morning transport in the heart of Sydney was brought to a standstill on Tuesday morning when a maintenance vehicle derailed between Circular Quay and Wynyard stations.

While no "workers were injured" during the incident according to the New South Wales (NSW) State department of transport, the daily commute for Sydneysiders heading into the office was thrown into chaos with extensive delays in both directions across a number of different train lines.

Urged to make "alternative travel arrangements" where possible, angry commuters took to social media to vent their frustration.

"The old saying goes that there are only two certainties in life: death & taxes. I'd like to add a third: Sydney trains being delayed," one man posted to Twitter.

But Rail, Tram and Bus Union (RTBU) NSW Secretary Alex Claassens said while he understands the frustrations "we're urging commuters to try and keep their cool and show respect for workers during this difficult time," he said in a statement, adding that the RTBU would launch a full investigation into how the derailment occurred.

The incident comes just two weeks after two people were killed when an interstate train traveling from Sydney to Melbourne derailed near the township of Wallan.

Transport NSW believes services will be back to normal before the afternoon peak.