Beast From 20,000 Fathoms (1953)

Nuclear physicist Paul Nesbitt sees what he believes to be a giant monster after an atomic bomb test in the arctic. The only other witness is killed when he is covered by ice. When Nesbitt returns to the States he tries to convince the world that he did see the monster. He even tries to convince paleontologist Thurgood Ellison. The only person who will believe him is Ellison's assistant, Lee Hunter. Ellison is finally convinced when Nesbitt and a survivor of a ship that was attacked by the monster both identify the monster as a rhedosaurus. Eventually the monster makes its way to New York where it kills several people, not only by devouring them or crushing them with its sheer weight but through a very virulent disease which is contained in its blood.