tourist visa extension in Ningbo

hi i am Thai national and will visit china on tourist visa and I will stay in Ningbo,Zhejiang, i ahve some friends in Ningbo ,My question is if i apply for extension,so where should i apply for extension ? i heard it is only possible in Shanghai ,Beijing and Guangzhou . But i read here that it could be apply in local PSB. so can i apply in Ningbo for L type extension? your earliest response will be highly appreciated.

regards
Siriya