Possible meanings are 1) the earthquake causing the hills to crumble to pieces is spoken of as if the hills were melting or 2) the water from the storms coursing down the hills and causing them to erode is spoken of as if the hills were melting. (See: [[rc://en/ta/man/jit/figs-metaphor]])
Here the word "world" refers to the inhabited places on the earth. The verb for this phrase is understood from the previous phrase. Alternate translation: "the world shakes and all the people who live in it collapse" (See: [[rc://en/ta/man/jit/figs-ellipsis]])