The study by the federally-funded Fred Hutchinson Cancer Center in Seattle found an estimated 1.87 million excess deaths from all causes occurred among people over 30 years of age between December 2022 and January 2023.
The paper, published in the journal JAMA Network Open, said that the deaths were observed in all provinces in mainland China except Tibet.
China in December last year removed its "zero-Covid", which aimed at stopping the spread of virus by imposing strict lockdowns, mass testing and other regulations.
The rules were dismantled following rare protests against the administration's orders that the 1.4 billion residents were religiously made to follow for three years since the onset of the pandemic in 2020.
The Communist government previously disclosed 60,000 Covid-related deaths that were recorded in health facilities from early December to the middle of January.
Once the restrictions were lifted, Beijing stopped its precise tracking of the virus, creating uncertainty about deaths related to Covid-19.
In February, China's top leaders declared a "decisive victory" over Covid.
In the study, researchers performed statistical analysis using information from published obituaries and data from searches on Baidu, a popular Chinese internet search engine.
"Our study of excess deaths related to the lifting of the zero-Covid policy in China sets an empirically derived benchmark estimate.
"These findings are important for understanding how the sudden propagation of Covid-19 across a population may impact population mortality," researchers wrote.
Joseph Unger, the senior author of the paper, said despite China being the first place to be hit by Covid-19, it was able to quickly suppress the disease through stringent measures over an extended period.
“Because the Chinese population had been largely shielded from infection with limited natural immunity and was not fully or well vaccinated, the sudden introduction of widespread Covid-19 infection had a devastating impact.” the biostatistician and health services researcher at Fred Hutchinson Cancer Center, added.
In a rare move, one Chinese province briefly published data on its website in July showing cremations jumped 70 per cent in the first quarter of this year, but was later taken down.
The World Health Organization (WHO) estimates the number of Covid-related deaths in China to be 121,628 out of almost seven million.
According to the Johns Hopkins University, the US has the highest number of confirmed deaths at 1,123,836, followed by Brazil and India.