Sydney’s public transport patronage has fallen by about three-quarters amid the coronavirus pandemic, with the fewest number of people using the network in almost a century.

About 51 million fewer trips were taken on Sydney's rail, bus and ferry network last month compared to March 2019, as cities across Australia shut down and unemployment rose.

The last time so few people were travelling on the city’s rail network was the 1920s, said University of Technology Sydney transport expert Mathew Hounsell.

“Transport is a derived need. Road and rail usage drop dramatically during recessions,” he said.