The US Commerce Department issued an order on Friday (Sep 18) that will bar people in the United States from downloading Chinese-owned messaging app WeChat and video-sharing app TikTok starting on Sep 20.

Commerce officials said the ban on new US downloads of TikTok could be still rescinded by President Donald Trump before it takes effect late Sunday as TikTok owner ByteDance races to clinch an agreement over the fate of its US operations.

ByteDance has been talks with Oracle Corp and others to create a new company, TikTok Global, that aims to address US concerns about the security of its users' data. ByteDance still needs Trump's approval to stave off a US ban.

"We disagree with the decision from the Commerce Department, and are disappointed that it stands to block new app downloads from Sunday and ban use of the TikTok app in the U.S. from Nov. 12," the company said in a statement. "We will continue to challenge the unjust executive order."

China's Commerce Ministry expressed its "resolute opposition" and urged the United States to stop its bullying and wrongdoing.

"If the U.S. side obstinately clings to its course, China will take necessary measures to resolutely safeguard the legitimate rights and interests of Chinese companies," it said, without elaborating.

Commerce officials said they will not bar additional technical transactions for TikTok until Nov 12, which gives the company additional time to see if ByteDance can reach a deal for its US operations. "The basic TikTok will stay intact until Nov 12," Commerce Secretary Wilbur Ross told Fox Business Network.

The department said the actions will "protect users in the US by eliminating access to these applications and significantly reducing their functionality."

Oracle shares fell 1.6 per cent after the news in pre-market trading.

The Commerce Department order will "deplatform" the two apps in the United States and bar Apple's app store, Google Play and others from offering the apps on any platform "that can be reached from within the United States," a senior Commerce official told Reuters.

The order will not ban US companies from doing businesses on WeChat outside the United States, which will be welcome news to US firms like Walmart and Starbucks that use WeChat's embedded 'mini-app' programmes to facilitate transactions and engage consumers in China, officials said.