Beijing has included its South China Sea territorial claims on maps printed inside new Chinese passports, infuriating at least one of its neighbours.

Vietnam has formally complained to Beijing about the new passports. “The Vietnamese side has taken note of this matter and the two sides are discussing it, but so far there has been no result,” said Vietnam’s embassy in Beijing.

Other countries that have clashed with China over the resource-rich region are also worried that Beijing is seeking implicit recognition of its territorial claims through the passports, which would be stamped every time a Chinese citizen visits. “This is viewed as quite a serious escalation because China is issuing millions of these new passports and adult passports are valid for 10 years,” said one senior Beijing-based diplomat who asked not to be identified because of the sensitivity of the issue. “If Beijing were to change its position later, it would have to recall all those passports.”