Workers removed the US insignia from the consulate in the Chinese city of Chengdu on Saturday, one day after Beijing ordered its closure as relations deteriorated in a Cold War-style standoff.
The Chengdu mission was ordered shut in retaliation for the forced closure of Beijing's consulate in Houston, Texas, with both sides alleging the other had endangered national security.
The deadline for the Americans to exit Chengdu remained unclear, but AFP reporters saw a worker on a small crane removing a circular US insignia from the front of the consulate, leaving just a US flag flying.
Three moving company trucks entered the US consulate building Saturday afternoon, and cleaners were seen carting large black rubbish bags from the consulate in the early hours of the morning. One of them split and appeared to contain shredded paper.
At least ten bags were removed from the building.
Other staff were seen carrying boxes, moving trolleys and wheeled suitcases inside the building.
Beijing says closing the Chengdu consulate was a "legitimate and necessary response to the unreasonable measures by the United States", and has alleged that staff at the diplomatic mission endangered China's security and interests.
Washington officials, meanwhile, said there had been unacceptable efforts by the Chinese consulate in Houston to steal US corporate secrets and proprietary medical and scientific research.
The last Chinese diplomats left the Houston consulate on Friday as a 72-hour deadline to close the mission passed. Officials there were seen loading large sacks of documents and other items onto trucks, and throwing some in bins.
Beijing said Saturday that US agents "forcibly" entered the Houston consulate.
The building "is China's national property", the statement read, citing the Vienna Convention on Consular Relations and the Sino-US Consular Treaty. It added that the United States "must not infringe on the premises ... in any way".
"China has expressed its strong dissatisfaction and firm opposition to the US forcibly entering the Chinese Consulate General in Houston and has lodged solemn representations".
The statement added that "China will make a proper and necessary response in this regard".
Tensions have soared between the two powers on a range of fronts including trade, China's handling of the novel coronavirus and a tough new security law for Hong Kong, with US officials this week warning of a "new tyranny" from China.
Closing the US consulate in Chengdu was a "legitimate and necessary response to the unreasonable measures by the United States", the foreign ministry said Friday.
"The current situation in China-US relations is not what China desires to see, and the US is responsible for all this", it said.
Foreign ministry spokesman Wang Wenbin told reporters that some US staff in the Chengdu consulate "were engaged in activities outside of their capacity, interfered in China's internal affairs, and endangered China's security and interests".
The Chengdu consulate, established in 1985, has been at the centre of past controversy. It was included on a top-secret map leaked by intelligence analyst Edward Snowden showing US surveillance worldwide.
The mission was also where senior Chinese official Wang Lijun fled in 2012 from his powerful boss Bo Xilai, who was then head of the nearby metropolis Chongqing, and has since been jailed for life for corruption.