Underreporting of infections leads to a overestimated mortality rate, underreporting of deaths leads to an underestimed mortality rate.
So unless you believe authorities are getting with hiding hundreds of deaths at hospitals being under international scrutiny, while simultaneously hiding the fact that dead people pile up at their homes, this theory seems kind of unlikely. Especially since international numbers outside of mainland China are more or less in line.
Test your information against samples from people with relations to ground-truth. Then you can panic.
But hey, you want to panic, go for it. But do it for yourself. Because now the "independent" media, the "propaganda" and the WHO numbers are more or less the same.