A man has severed his foot after falling from a train platform at Sydney's Town Hall station.

It is believed the man, aged in his 60s, became stuck under one of the trains.

He suffered a part amputation of one of his feet and serious head and leg injuries, a spokesperson for NSW Ambulance said.

Paramedics rushed the man to Royal Prince Alfred Hospital in Camperdown, where he is in a stable condition.

A man was stuck under a train at Town Hall station in Sydney. (9News)"Sydney Trains can confirm an elderly male customer has been transported to hospital with injuries after an incident at 12:07pm today at Town Hall Station," A Sydney Trains spokesperson told nine.com.au.

"While circumstances are still being investigated, it would appear the man accidentally fell onto the tracks into the path of an oncoming train.

"Sydney Trains would like to thank our staff, members of the public, and emergency services that worked quickly to come to the injured man's assistance."  

Customers are advised to allow extra travel time and to plan their journey ahead by visiting transportnsw.info or using the trip planning apps on their mobile devices.