The user said the photo of the T-shirt was taken at an outlet store in Canada.
Marriott and Gap aren't alone in causing offence to China, Delta Air Lines recently issued a public apology for what it described as a "grave mistake" after listing Taiwan and Tibet as independent countries on its website.
Photographs of a T-shirt that the clothes brand had apparently sold in Canada were circulating on China's Internet, with many online comments saying that southern Tibet, Taiwan and the South China Sea were missing.
"Upon the realization that one of our T-shirts sold in some overseas markets mistakenly failed to reflect the correct map of China, we urgently launched an internal investigation across the group and have made a decision to immediately pull back this T-shirt from all the concerned global markets", Gap said in a statement.
"Upon the realization that one of our T-shirts sold in some overseas markets mistakenly failed to reflect the correct map of China, we urgently launched an internal investigation across the group and have chose to immediately pull back this T-shirt from all the concerned global markets", the company said in a statement.
In response, Gap said it would implement "rigorous reviews" to prevent repeating the incident and that it respects China's "sovereignty". "We sincerely apologize for this unintentional error".
The printed map did not include Taiwan, a self-ruled island considered Chinese territory by Beijing, the capital.
Other than Marriott, the Chinese websites of US-based medical supplies company Medtronic and Spanish fashion brand Zara were found to have listed Taiwan as a "country" or as "Republic of China" and were ordered by the government to make corrections and apologise, state media Xinhua Agency has reported.
The name change came in the wake of letters sent by China's Civil Aviation Administration in late April, pressuring 36 American and worldwide airlines to remove references to Taiwan, Hong Kong and Macau as countries on their websites and marketing materials.
China then issued new passports in 2012 that carried a map laying claim to several disputed islands and territories, infuriating countries across Asia.
Taiwan's foreign ministry said it was "deeply concerned" about Air Canada's move to refer to Taiwan as part of China in its materials.