HQ-64
HQ-64 is the improvement of HQ-6, utilizing the experience gained from LY-60, with the firepower doubled when the number of missiles for each truck mounted launcher is increased from two to four, and MLR is replaced by TELs. Both the missile and TELs are directly developed from LY-60. Although the missile is smaller than that of HQ-6, the performance actually improved due to technological advance. HQ-64 passed state certification test and was accepted into Chinese service in 2001. The reaction time for the system in fully automated mode is 9 seconds and the maximum speed of the missile is increased to Mach 4. Other improvements is mainly concentrated on ECCM capability, and many Chinese internet sources have claimed (yet to be confirmed) that HQ-64 is derived from HQ-6-4, meaning 4 missiles (for each launcher) version of HQ-6, which only had two missiles for each launcher.
Read more about this topic: LY-60 / FD-60 / PL10