Do you mean fly from Singapore to Nanning or other cities? It seems there is no direct flight between them. Holding singapore passport, you will do not need a visa to visit China except Tibet in 15 days. If your stay time is longer than 15 days, you need to go to CVASC or Chinese embassy in Singapore(https://www.travelchinaguide.com/embassy/singapore.htm) to apply for a tourist visa.