Horror Express

The 1972 Spanish/British horror film Horror Express stars Christopher Lee, Peter Cushing, Alberto de Mendoza, and Telly Savalas. From Wikipedia:

In 1906, Saxton (Christopher Lee), a renowned British anthropologist, is returning to Europe by the Trans-Siberian Express from China to Moscow. With him is a crate containing the frozen remains of a primitive humanoid creature that he discovered in a cave in Manchuria. He hopes it is a missing link in human evolution. Doctor Wells (Peter Cushing), Saxton's friendly rival and Royal Society colleague, is also on board but travelling separately. Before the train departs Shanghai, a thief is found dead on the platform. His eyes are completely white without irises or pupils, and a bystander initially mistakes him for a blind man. A monk named Father Pujardov (Alberto de Mendoza), the spiritual advisor to the Polish Count Marion Petrovski (George Rigaud) and Countess Irina Petrovski (Silvia Tortosa), who are also waiting to board the train, proclaims the contents of the crate to be evil. Saxton furiously dismisses this as superstition. Saxton's eagerness to keep his scientific find secret arouses the suspicion of Wells, who bribes a porter to investigate the crate. The porter is killed by the ape-like creature (Juan Olaguivel) within, which then escapes the crate by picking the lock.

The creature finds more victims as it roams the moving train, each victim being found with the same opaque, white eyes.

There's more to the plot summary, but you don't need it. Just watch the movie.