Extended Visa

In the past, the government allowed extensions on M Visa(aka business visa) by the corresponding visa duration. 30-day M visas get 30 day extensions. 60-day M visas get 60 day extensions. 
However, that option is no longer available. The government is very strict on this issue now. 
It seems it will be easier and faster to go to a neighboring country and get a tourist visa for China. 
Nonetheless, if you want to test your luck and extend.. here are the list of documents that were required to extend an M visa back in the days…:
1. Passport with valid M visa (in green color) issued from outside of China
2. 2 Passport Photographs (size 4.5cm*3.5cm)
3. Local Shanghai Registration Form Of Temporary Residence( up to date )
4. Copy of the shanghai company business license
5. Copy of the shanghai company enterprise code license
6. Shanghai company invitation letter to state you are the client of them -with official stamp
7. Shanghai company assignment letter with official stamp to assign VisaInChina as a visa agent for your M visa extension (Print out and stamp it directly, don’t modify)
8. Copy of the shanghai company official invitation letter which you used to apply your M visa in the Chinese Embassy/Consulate outside. 
 
sourced from: http://www.visainchina.com/fvisa.htm
You could also just visit the Shanghai exit-entry bureau in pudong. “Inquiry” booths #14-16 answer any questions you may have. So asking them directly would yield the most accurate answer. 
I would suggest consulting with an agency like VisaInChina. Visainchina.com is owned by a guy called Magic. Most expats who have lived in Shanghai know Magic or heard about him. He’s legit. 
They are usually pretty good with answering general questions as well. You can email his team: [email protected]
Good luck, Tom!!