Vietnamese Tones

Tones

Generally, the Northern varieties have six tones while those in other regions have five tones. 

The hỏi and ngã tones are distinct in North and some North-central varieties (although often with different pitch contours) but have merged in Central, Southern, and some North-central varieties (also with different pitch contours). 

Some North-central varieties (such as Hà Tĩnh Vietnamese) have a merger of the ngã and nặng tones while keeping the hỏi tone distinct. Still other North-central varieties have a three-way merger of hỏi, ngã, and nặng resulting in a four-tone system. 

In addition, there are several phonetic differences (mostly in pitch contour and phonation type) in the tones among dialects.

~Info courtesy of Wikipedia~