Jonah began to enter into the city a day's journey, and he cried out, and said, "Yet forty days, and Nineveh shall be overthrown!"
The same Hebrew word (haphak, overthrown, destroyed) describes the destruction of Sodom and Gomorrah in Genesis 19:25. Possibly Jonah expected God to destroy Nineveh as He had overthrown Sodom and Gomorrah.