Chinese state TV has showed what it asserts was "a routine rotation" of military troops and equipment into a garrison in Hong Kong.
This development is naturally raising concerns in the territory that has been rocked by pro-democracy protests for weeks and is due to hold another big rally on Saturday.
For more on this and other news around the world, let's turn to our Kim Da-mi.
Da-mi, tell us more.
Troops from mainland China moved into Hong Kong on Thursday for what they called a "routine rotation".
According to China's Xinhua News Agency, armored carriers, trucks and a patrol boat crossed the border from Shenzhen to Hong Kongfor the 22nd rotation of the People's Liberation Army's Hong Kong garrison.
The Hong Kong garrison highlighted that it was just another annual practice.
It added that troops stationed in Macao also completed a rotation on Thursday.
The soldiers in the new rotation were reportedly educated on Hong Kong's laws and vowed to defend the nation's sovereignty.
The longest protest in Hong Kong's history has sparked concerns Beijing may use its military from the mainland to crack down on protesters.
Meanwhile,Hong Kong police have banned a mass protest rally planned on Saturday over public safety concerns, but the protesters have vowed to demonstrate anyway.