The Waratah train hit the metal and concrete barrier at the end of platform 2 just before 10am, giving those on board injuries ranging from cuts and bruises to broken bones.

As it was designed to do, the buffer stop absorbed some of the impact of the crash and pushed the train slightly back, ensuring it remained on the track instead of derailing.

Sydney Trains chief executive Howard Collins said the train hit the buffer stop "pretty hard", but it "worked effectively and restrained the train".

Superintendent Paul Turner, the incident commander for NSW Ambulance, said: "Things could've been much, much worse."

According to Transport for NSW, buffer stops are installed at the end of rail tracks to stop trains running off the end and crashing into "adjacent structures".

The buffer stops are usually hydraulic, which helps to dissipate some of the energy of impact. Their aim is to safely stop an "overrunning train" while keeping damage to the train and injury to its passengers at a minimum.

Buffers, which can be made of wood or metal, are designed to withstand being hit by a range of fully loaded trains, including the Waratah trains, which weigh 562 tonnes when filled with people.

Design specifications by Transport for NSW detail that the buffers are designed for a train travelling at the highest possible speed, taking into account factors such as brake failure and how steep the track is at individual stations.

Buffer stops are attached to an "end impact wall", which takes any leftover impact from the train.

The wall can withstand up to 5000 kilonewtons of force, while the buffer itself has a minimum braking capacity of 2500 kilonewton metres.