TikTok and WeChat will be banned from US app stores from Sunday, unless President Donald Trump agrees to a last-minute deal.
The Department of Commerce said it would bar people in the US from downloading the messaging and video-sharing apps through any app store on any platform.
The Trump administration says the companies threaten national security and could pass user data to China.
But China and both companies deny this.
WeChat will effectively shut down in the US on Sunday, but people will still be able to use TikTok until 12 November, when it could also be fully banned.
If a planned partnership between US tech firm Oracle and TikTok owner ByteDance is agreed and approved by President Trump, the app would not be banned.
It is not yet clear whether Mr Trump will approve the deal, but he is expected to review it before the Sunday deadline.
The ban order from the Department of Commerce follows President Trump's executive orders signed in August. It gave US businesses 45 days to stop working with either Chinese company.
What does the order say?
"At the president's direction, we have taken significant action to combat China's malicious collection of American citizens' personal data," the US Department of Commerce Secretary Wilbur Ross said in a statement.
The department acknowledged that the threats posed by WeChat and TikTok were not identical but said that each collected "vast swathes of data from users, including network activity, location data, and browsing and search histories".
While WeChat closes on Sunday, TikTok users will still be able to use their app virtually as normal, although they will not be able to download new updates.
"The President has provided until November 12 for the national security concerns posed by TikTok to be resolved," the commerce department said.
Why does the US want the apps banned?
The Trump administration has repeatedly said the apps are a threat because of their collection of data.
Friday's statement from the commerce department said the governing Chinese Communist Party "has demonstrated the means and motives to use these apps to threaten the national security, foreign policy, and the economy of the US."
President Trump has repeatedly criticised China since taking office, accusing Beijing of unfair trading practices and intellectual property theft.
ByteDance has denied that it holds any user data in China, saying it is stored in the US and in Singapore. Tencent, which owns WeChat, has said that messages on its app are private.
While TikTok has millions of users in the US, it is not clear how many of WeChat's billion users are based outside China, although it is likely to be a significant number.
But the US is not the only country concerned about the companies. India has already banned TikTok and WeChat, as well as dozens of other Chinese apps. The government in Delhi said the apps were "prejudicial to sovereignty and integrity of India, defence of India, security of state and public order".
The UK Information Commissioner's Office, a privacy watchdog, is also currently investigating the app.
Hina Shamsi, director of the American Civil Liberties Union's National Security Project said the order violated First Amendment rights.
"The order also harms the privacy and security of millions of existing TikTok and WeChat users in the United States by blocking software updates, which can fix vulnerabilities and make the apps more secure," she said.
"To truly address privacy concerns raised by social media platforms, Congress should enact comprehensive surveillance reform and strong consumer data privacy legislation."