Beijing's zero-COVID strategy has come under strain since March as over 100,000 cases in Shanghai have seen its 25 million inhabitants locked down in phases, AFP reported.
The US Embassy said Saturday it would permit non-essential employees to leave its consulate in Shanghai due to the case surge, warning citizens in China they may face "arbitrary enforcement" of virus curbs.
In response, Beijing expressed "strong dissatisfaction and firm opposition to the US side's groundless accusations about China's epidemic control policy", according to a statement issued Saturday on the Foreign Ministry's website.
"This is the US's own decision. However, it must be pointed out that China's epidemic control policy is scientific and effective," ministry spokesman Zhao Lijian said, adding that Beijing had lodged "solemn representations" with American counterparts.
"We have full confidence that Shanghai and other places will overcome this round of the epidemic."
China is sticking fast to a policy of snap lockdowns, mass testing and travel restrictions to staunch the spread of the virus even as Shanghai's daily case numbers have spiraled under an Omicron-fuelled wave.
The business hub reported a record 24,943 new infections on Sunday – mostly asymptomatic, accounting for over 90 percent of the national total.
Authorities have readied tens of thousands of new beds in over 100 makeshift hospitals as part of a policy of isolating every person who tests positive for the virus – whether or not they show any symptoms.
City health official Wu Qianyu said during a Sunday press conference the city "would not relax in the slightest".
Major online delivery platforms said they would bolster food stocks and draft in thousands of drivers to strengthen the supply of basic goods.
In an interview with a local news outlet on Saturday, Zhang Wenhong – a top doctor in Shanghai's pandemic fight – acknowledged the impact on the health care system but said "realising dynamic zero ... will help to resume normal medical order as early as possible".