US navy hong kong
Mere hours after President Trump tweeted that US intelligence had confirmed the buildup of Chinese troops on the border with Hong Kong, US defense officials warned that Beijing had refused two US Navy ships permission to make port stops in Hong Kong in the coming weeks, a sign that President Xi is none too pleased with how the US has handled itself during the anti-extradition bill protests that have swept Hong Kong over the past ten weeks.

Beijing has repeatedly warned the US to stop interfering with Taiwan and Hong Kong, or else face consequences, including the implicit threat of force.

Meanwhile, China confirmed that it denied the requests made by the US Navy.
Commander Christensen, Deputy Spokesperson, US Pacific Fleet: The Chinese Government denied requests for port visits to Hong Kong by the USS Green Bay and USS Lake Erie, which were scheduled to arrive in the next few weeks.
We note that the last time the US allowed a naval destroyer from the "Chinese People's Liberation Army Navy" to make port visits in the USA was December 2016:
Three Chinese Navy ships arrived in San Diego as part of a routine port visit that will last from December 6 to 9.

Two Jiangkai II-class frigates Yancheng (FFG 546) and Daqing (FFG 576), and the Fuchi-class oiler Tai Hu (AOR 889) were hosted by the U.S. Navy destroyer USS Cape St. George (CG 71) in San Diego, where sailors from both navies will participate in sporting events and cultural exchanges.

"Practical cooperation, such as port visits and key leader engagements, helps us enhance transparency and mitigate risks when we operate at sea," said Rear Adm. James S. Bynum commander, Carrier Strike Group Nine.

"Continuous dialogue is necessary to find where we share interests and also to address disagreements candidly if they arise."
A spokesman for Beijing warned that they're worried the presence of US ships might embolden protesters, meanwhile, US officials have warned that they prefer not to make shipfall in areas where unrest is brewing.