According to search results of "公安机关适用刑事羁押期限规定" (Provisions of Criminal Detention Duration for Public Security Organizations) yielded by the Baidu search engine, normal detention without formal charges may last from one to three days. For reasons such as preventing further crimes or escape, a special request granted by authorities of a township or above (such as municipality or province) will allow the detention without charge to be extended to 30 days.
Below are the direct quote from the document dated 27 January 2006:
公安机关适用刑事羁押期限规定Below is the translation:
Provisions of Criminal Detention Duration for Public Security Organizations
1. Released by Ministry of Public Security on 27 January 2006
2. The Public Through  No. 17
3. Shall come into force since 1 May 2006
Article VI. When a public security authority at the level of a township or above makes a decision to approve a detention, the accompanying report should indicate the length of the detention time of one to three days. If there is a need to extend the detention to one to four days, or to thirty days, follow the request to prolonged detention procedures.
Article IX. If it is not possible to ask the People's Procuratorate to examine and approve an arrest within three days after the suspects is detained, and if there is evidence that the criminal suspect may escape and repeatedly commit crimes, or commit gang crimes, the detention, after being reported to the public security authority at the level of a township or above, and if approved by the authorities, may be immediately extended to the thirty days.
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