The phonological structure of each syllable consists of a nucleus consisting of a vowel (which can be a monophthong, diphthong, or even a triphthong in certain varieties) with an optional onset or coda consonant as well as a tone. There are some instances where a vowel is not used as a nucleus. An example of this is in Cantonese, where the nasal sonorant consonants /m/ and /ŋ/ can stand alone as their own syllable.
Across all the spoken varieties, most syllables tend to be open syllables, meaning they have no coda, but syllables that do have codas are restricted to /m/, /n/, /ŋ/, /p/, /t/, /k/, or /ʔ/. Some varieties allow most of these codas, whereas others, such as Mandarin, are limited to only two, namely /n/ and /ŋ/. Consonant clusters do not generally occur in either the onset or coda. The onset may be an affricate or a consonant followed by a semivowel, but these are not generally considered consonant clusters.Free quote
The number of sounds in the different spoken dialects varies, but in general there has been a tendency to a reduction in sounds from Middle Chinese. The Mandarin dialects in particular have experienced a dramatic decrease in sounds and so have far more multisyllabic words than most other spoken varieties. The total number of syllables in some varieties is therefore only about a thousand, including tonal variation.
All varieties of spoken Chinese use tones. A few dialects of north China may have as few as three tones, while some dialects in south China have up to 6 or 10 tones, depending on how one counts. One exception from this is Shanghainese which has reduced the set of tones to a two-toned pitch accent system much like modern Japanese.