President Donald Trump said Tuesday China is moving troops to the border with Hong Kong, where anti-government protests staged at the airport led to extensive flight cancellations.

"Our Intelligence has informed us that the Chinese Government is moving troops to the Border with Hong Kong," Trump said in a Twitter post, without providing details.

"Everyone should be calm and safe!" he wrote.

(File photo)

Riot police briefly clashed with pro-democracy protesters outside Hong Kong International Airport for the second day on Tuesday, though calm returned to the airport in the early hours of Wednesday.

Earlier Tuesday, Trump called the Hong Kong protests "a very tough situation" and "a very tricky situation." He urged relevant parties to address the issue peacefully.

"I hope it works out for liberty. I hope it works out for everybody, including China," he told reporters in New Jersey.

"I hope it works out peacefully. I hope nobody gets hurts. I hope nobody gets killed."

In a related move, U.S. Secretary of State Mike Pompeo met with China's top foreign policy official Yang Jiechi on Tuesday in New York, and apparently discussed the situation in Hong Kong.

Pompeo and Yang, director of the Office of the Foreign Affairs Commission of the Communist Party of China Central Committee, "had an extended exchange of views on U.S.-China relations," the State Department said, without elaborating.