Dozens of Chinese military vehicles entered Hong Kong on Thursday for what was described as a "routine annual rotation" but which caused widespread concern amid ongoing pro-democracy protests.

State news agency Xinhua reported that the Hong Kong Garrison of the Chinese People's Liberation Army conducted the 22nd rotation of its members since it began the process in 1997. The outlet said the rotation was approved by the Central Military Commission and that it is in line with China's law on garrisoning within Hong Kong.

People's Daily China tweeted videos and photos of the operation showing military vehicles being transported through the streets of Hong Kong.

While China said it was an approved routine procedure, some saw it as a display of the country's power and willingness to respond with force to the demonstrations that have been taking place for the past 12 weeks in Hong Kong.

Earlier this month, photos showed Chinese armored military vehicles in a sports stadium near the country's border with Hong Kong.