The 2004 Sri Lanka tsunami train wreck is the largest single rail disaster in world history by death toll, with 1,000 fatalities or more. It occurred when a crowded passenger train (No 50, Matara Express) was destroyed on a coastal railway in Sri Lanka by a tsunami that followed the 2004 Indian Ocean earthquake.
https://en.wikipedia.org/wiki/2004_Sri_Lanka_tsunami_train_wreck