He cited several examples of Chinese aggression against the United States: The Justice Department has charged a rising number of USA academics for transferring U.S. taxpayer-funded intellectual property to China.
He said, "China poses the greatest threat to America today, and the greatest threat to democracy and freedom world-wide since World War Two".
Writing in the Wall St Journal, John Ratcliffe said China was growing its power by stealing USA secrets and then replacing United States firms in the market.
Mr Ratcliffe and other USA officials have said that China has stolen sensitive United States defence technology to fuel Mr Xi's aggressive military modernisation plan and they allege that Beijing uses its access to Chinese tech firms, such as Huawei, to collect intelligence, disrupt communications and threaten the privacy of users worldwide.
The Director of National Intelligence said China had replaced Russian Federation and counter-terrorism as the main focus of USA intelligence activities.
Demers advocated for the incoming Biden administration to remain vigilant to foreign influence threats, noting that the "breadth of foreign influence" engaged in by the Chinese government has not been "exposed publicly as it probably will be over the coming years". Chinese academics have also faced greater scrutiny, while dozens of journalists with state media have been forced to return home and visa restrictions placed on those remaining, prompting retaliation from Beijing.
"(Ratcliffe) only continues to repeat lies and rumours to slander and discredit China, and wantonly play up the Chinese threat", said Chinese foreign ministry spokesman Hua Chunying.
The nation's top intelligence official just unloaded on China in unusual fashion.
Coronavirus likely in USA as early as December 2019
These new findings are yet another illustration of how complicated it is to solve the scientific puzzle of virus source tracing. Despite the findings, widespread community transmission in the US was unlikely until late February, the authors said.
It said the party and its members have worked in the USA to influence Americans through propaganda, and that the party is sending agents to monitor the activities of Chinese-Americans.
Ratcliffe said he has personally briefed members of Congress about how China is using intermediaries to lawmakers in an attempt to influence legislation.
Earlier in June, the Defense Department added 20 Chinese companies to the blacklist, including China's largest telecom operator China Mobile, the world's third-largest server provider Inspur, global No. 1 surveillance camera provider Hikvision, and Huawei.
While the list did not initially trigger any penalties, a recent executive order by Republican President Donald Trump will prevent USA investors from buying the firms' securities from late next year.
"This is an escalation of their political oppression towards China and China is firmly opposed to that", she said.
The travel restrictions came as the USA also said it would block imports of cotton it says are harvested with "slave labor" in the western Xinjiang region of China.
The restrictions are the latest punitive measure taken against China's leadership and economy amid sharpening disputes over human rights, the coronavirus pandemic, trade, technology, Taiwan and a host of other issues.
Congress and the Trump administration have sought increasingly to curb the US market access of Chinese companies that do not comply with rules faced by American rivals, even if that means antagonizing Wall Street.