For foreigners entering the Chinese mainland with a visa, if the original reason for entry has not yet been terminated or if for other legitimate reasons that require they to stay beyond the expiration date specified in the visa without the need to change the type of visa, they may apply for extending the visa. Documents required for visa extension are as follows:
(I) Valid passports or other international travel documents;
(II) A completed Foreigner Visa Application Form, and a 33×48mm bareheaded color ID photo taken recently against a white background (free on-site photography is available);
(III) Supporting documents concerning the reason for the visa extension application;
(IV) Supporting documents required for other procedures.

For the application documents required for visa extension, processing procedures and methods, fee basis and standards, etc., they can visit the official website of China's National Immigration Administration and refer to the Guide on Visa Extension, Replacement and Reissuance for Foreigners under "Services". The requirements for the photos for travel documents can be found in the Guidelines for Travel Documents Photographs in the "Services" section. Additionally, they can find the office address and contact information of local exit-entry reception halls in "Office Enquiries" under "Services". They can also reach out to the 12367 service platform for further information via the hotline or online portal.

Source：Ministry of Commerce of the People's Republic of China