Armed conflict has raged in Myanmar's northern Shan state since October, when an alliance of ethnic minority groups launched an offensive against the military junta.
Several Chinese media outlets reported on Wednesday that an artillery shell from Myanmar had fallen across the border in the town of Nansan in China's Yunnan province, where it exploded and caused injuries to multiple people.
AFP was not able to independently verify the reports or accompanying images posted on social media.
Asked about the reports at a regular press briefing on Thursday, foreign ministry spokesman Wang Wenbin said China "expresses strong dissatisfaction that the armed conflict has caused Chinese casualties," adding that Beijing had "made solemn representations to the relevant parties."
"China once again demands that all parties in the northern Myanmar conflict immediately cease hostilities and take practical measures to prevent further pernicious incidents that endanger peace and tranquillity on the border," Wang said.
"China will take all necessary measures to safeguard the security of its citizens' lives and property," he said.
Wang did not specify how many people had been killed or wounded in the incident.
The ethnic alliance has seized several towns and border hubs vital for trade with China in what analysts say is the biggest military challenge to the junta since it seized power in 2021.
Last month, Beijing said it had mediated talks between the Myanmar military and the allied ethnic armed groups and reached an agreement for a "temporary ceasefire."
However, clashes have continued in parts of Shan state, and China's embassy last week asked its citizens to evacuate an area along the shared border owing to security risks.