DANDONG, China (Yonhap News) -- More than 100 Chinese soldiers took part in a river-crossing exercise on its Yalu River border with North Korea Tuesday, renewing speculation the Chinese military is preparing to defend against any influx of North Korean refugees following possible regime collapse in Pyongyang.

Uniformed soldiers wearing orange life vests could be seen building and rebuilding about a dozen pontoon bridges at various points along the Yalu River, which separates China and North Korea.

Each bridge stretched 20 to 30 meters, made up of six or seven sections connected to each other.

That section of the river that separates the Chinese city of Dandong and the North Korean city of Sinuiju is only 400 to 500 meters wide.

Chinese troops have been observed during similar exercises in the past, with Japanese media outlets reporting one such in July 2004. The Chinese state-run media denied such exercises had taken place, and the Beijing government remained silent.

Media reports have claimed the drills are to prepare China for regime collapse in Pyongyang, which it fears will spark a massive influx of North Korean refugees across their shared border. The reports claimed Chinese troops could cross into North Korea in such an event to stem the flow of refugees.

Dandong residents told Yonhap News Agency the exercises take place on a regular basis and usually in the summer.

“The drill today started in the morning, but I have seen Chinese troops conduct similar exercises on the Yalu River about two or three more times in previous years,” said one resident, who spoke on condition of anonymity.

As the exercises took place, not much activity could be detected from the other side of the river in Sinuiju, aside from a few North Korean cargo ships anchored at a dock.

Dandong is an economic and political hot spot in relations between China and North Korea, as it serves as the biggest hub for bilateral trade and a major destination for North Korean defectors seeking to resettle in South Korea.

China is North Korea‘s last remaining major ally and the two countries are bound by a treaty that pledges military support in the event of a war on either side.