Chinese-owned app TikTok resumed its service for 170 million users across the USA hours after President-elect Donald Trump vowed he would issue an executive order to give it a reprieve after taking office following his inauguration on Monday.

The app stopped its operation in the US on Saturday after a law banning it on national security grounds became effective.

Trump said implementation of the law would be delayed and TikTok would be given time to reach a deal.

In his post on Truth Social,  Trump said: "I’m asking companies not to let TikTok stay dark! I will issue an executive order on Monday to extend the period of time before the law’s prohibitions take effect, so that we can make a deal to protect our national security."

He said: "The order will also confirm that there will be no liability for any company that helped keep TikTok from going dark before my order."

Trump said he wants 50 percent American ownership in the popular platform.

Trump, who will take charge of his office for the second term, further wrote: "I would like the United States to have a 50% ownership position in a joint venture."

"By doing this, we save TikTok, keep it in good hands and allow it to say up.  Without U.S. approval, there is no Tik Tok.  With our approval, it is worth hundreds of billions of dollars - maybe trillions," he said.

"Therefore, my initial thought is a joint venture between the current owners and/or new owners whereby the U.S. gets a 50% ownership in a joint venture set up between the U.S. and whichever purchase we so choose," he said.

TikTok thanks Trump

Meanwhile, after the app was restored a popup message was reportedly seen by millions of users thanking Trump by name.

In a statement, the company thanked the incoming president for "providing the necessary clarity and assurance" and said it would work with Trump "on a long-term solution that keeps TikTok in the United States", reported BBC.

The law, which was signed by outgoing President Joe Biden last year, needed Byte Dance, the parent company that owns TikTok, to divest the app by January 19 to avoid a ban.

The app has been facing intense scrutiny from US authorities who fear the Chinese government could demand user data or use the app to spread propaganda.