Using the same approach as the US could cause cases to rise to 637,155, while copying Britain would lead to 275,793 daily new cases.
China says the importance of containing local cases outweighs the disruptions caused by efforts to trace, isolate and treat the infected.
In the report published in China CDC Weekly by the Chinese Centre for Disease Control and Prevention, the mathematicians said China could not afford to lift travel restrictions without more efficient vaccinations or specific treatments.
Using data for August from the United States, Britain, Spain, France and Israel, the mathematicians assessed the potential results if China adopted the same pandemic control tactics as those countries.
China's daily new cases would reach at least 637,155 if it adopted the United States' pandemic strategy, the report said.
Daily cases would hit 275,793 if China took the same approach as Britain and 454,198 if it imitated France, it said.
"The estimates revealed the real possibility of a colossal outbreak which would almost certainly induce an unaffordable burden on the medical system," the report said.
China reported 23 new confirmed coronavirus cases for November 27, down from 25 a day earlier, its health authority said on Sunday.
The mathematicians cautioned that their estimates were based on basic arithmetic calculations and that more sophisticated models were needed to study the evolution of the pandemic if travel restrictions were lifted.
The World Health Organization (WHO) on Friday designated a new COVID-19 variant detected in South Africa with a large number of mutations as being "of concern", prompting some countries to impose travel curbs.
Several countries, including Australia, Brazil, Canada Iran, Japan, Thailand and the United States, have joined others, including the European Union and the UK, in imposing restrictions on southern African countries in response to warnings over the transmissibility of the new variant — against the advice of the WHO.
Israel said it would ban the entry of all foreigners into the country, making it the first country to shut its borders completely in response to the new variant.
The government said it would use counter-terrorism phone-tracking technology in order to contain the spread of Omicron.