It's not strictly correct. The correct version is "Do you want some more rice?" but people sometimes omit the do in speech, for brevity, since the meaning of the sentence is still obvious without it.

Thanks for the quick response.I thought the sentence should not have the word "some" if I were to use the word "more", which means the correct version is "do you want more rice?" rather than "do you want some more rice?"

1. "Do you want some more rice?" - this is the normal way to ask this question.
2. "Do you want some more rice?" - this is acceptable too, but to me, it sounds a bit curt.
3. "Would you like some more rice?" - this is a more polite way to ask the question.

The differences are subtle and may vary with location. In some countries