Extend stay period in China

Hi, I'm currently working in China for some business meeting in GZ.
My company helps meto get type M for 30 days, but now I need to extend my stay period here for another 30 days since I have some business that still needs to be take care of.
Do I have to submit all the requirements to extend my type?
And where should I go to request my visa extension ?
Since my company can't help me to arrange this but they do provide invitation letter that stated I need to extend my staying period here (currently I'm staying in Guangzhou)