Not all of the world was covered, but large parts. See link at post 28.
The author seems to suggest there was a worldwide flood.
19The water prevailed more and more upon the earth, so that all the high mountains everywhere under the heavens were covered. 20The water prevailed fifteen cubits higher, and the mountains were covered. 21All flesh that moved on the earth perished, birds and cattle and beasts and every swarming thing that swarms upon the earth, and all mankind; 22of all that was on the dry land, all in whose nostrils was the breath of the spirit of life, died. 23Thus He blotted out every living thing that was upon the face of the land, from man to animals to creeping things and to birds of the sky, and they were blotted out from the earth; and only Noah was left, together with those that were with him in the ark. Gen 7:19-23 NASB