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 Kong for the 22nd rotation of the People's Liberation Army's Hong Kong garrison.
Although it was 2 months early,the Hong Kong garrison said 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.
The longest protest in Hong Kong's history has sparked concerns Beijing may use its military from the mainland to crack down on protesters.
Shenzhen city announced plans to deploy 240-thousand citizens as volunteer police officers against the Hong Kong demonstrations.
Hong Kong police have banned a mass protest planned on Saturday over public safety concerns, but the protesters have vowed to demonstrate anyway.
Meanwhile, the police officer who fired a gunshot during a protest last weekend has been invited to Beijing's National Day celebrations in October.
Despite strong criticisms in Hong Kong against his behavior, Chinese media outlets praised the officer as a hero.
Kim Da-mi, Arirang News.