The claims were made in a new 96-page report published by the US House Foreign Affairs Committee. The committee is currently controlled by the Democrat party, though Republican members have authored the report.
It claims the pandemic could have been avoided altogether if China had acted more openly in its response.
It also slams the World Health Organisation, with authors accusing the international health watchdog of being “complicit” in spreading Chinese “propaganda”.
The report has been obtained ahead of its official release by the New York Post.
Tedros Adhanom Ghebreyesus, head of the World Health Organisation
Parts of it allegedly read: “It is beyond doubt that the CCP actively engaged in a cover-up designed to obfuscate data, hide relevant public health information, and suppress doctors and journalists who attempted to warn the world.
“Research shows the CCP could have reduced the number of cases in China by up to 95 percent had it fulfilled its obligations under international law and responded to the outbreak in a manner consistent with best practices.
“It is highly likely the ongoing pandemic could have been prevented.”
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The US was soon hit hard by the virus - a deserted Times Square in New York, March 22
The report mentions particular failures on China’s part, including the closure and deep-cleaning of a wet market in Wuhan where the virus is thought to have originated.
The report says this action will have removed “forensic evidence that may have provided insight” into how the outbreak started.
The Republicans also claim China knew the virus was probably very contagious when scientists analysed it initially, but did not immediately inform the WHO.
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The report claims China had covered up coronavirus data
Lawmakers behind the report have also called on Tedros Adhanom Ghebreyesus, Director-General of the WHO, to step down, the New York Post adds.
The committee publication reads: “Director-General Tedros should accept responsibility for his detrimental impact on the COVID-19 response and resign.”
China confirmed it was treating dozens of cases of pneumonia in Wuhan on New Year’s Eve, 2019, though the cause at the time was unclear.
Tedros Adhanom Ghebreyesus meets China's Xi Jinping in January
Coronavirus statistics graph
On January 2, the Central Hospital of Wuhan issued a ban on employees talking about the illness publicly, according to the British Foreign Policy Group.
On January 14, Hong Kong reporters were taken to a police station after attempting to record the inside of a hospital in Wuhan, the BFPG adds.
The first confirmed case in the US emerged on January 21st, with others also confirmed in Japan, South Korea and Thailand around that time.
The US is due to officially leave the WHO in July next year, after Mr Trump criticised the health body
At the time of writing, there have been a total of 31,091,469 cases of COVID-19, with 961,351 deaths, according to the European Centre for Disease Control.
Despite the criticism of the WHO, the report advises against the US pulling out of the organisation – something President Donald Trump has threatened to do.
It states the US can instead “drive forward the necessary reforms” to both the WHO and International Health Regulations.