ALXA LEAGUE, China — Work crews attempting to locate 47 people missing following a collapse at an open-pit mine in northern China have had to change their excavation methods in order to avoid causing more landslides, according to state media on Friday.

As of Thursday night, six people had been confirmed dead and six injured at the mine in Inner Mongolia's Alxa League, according to broadcaster CCTV.

With a large collapsed area at the mine, backhoes and bulldozers digging can cause more collapses. The crews are excavating by layers and making trapezoid-shaped descents to continue their search from both sides of the mountain, according to the report.

"It is very difficult to conduct rescue work," said Li Zhongzeng, the head of the Alshaa League in Inner Mongolia, to CCTV. "Rescue efforts from all over the world, including neighboring regions, are rushing to the scene."

At around 1 p.m. Wednesday, one of the pit's walls caved in, burying people and mining trucks below in tons of rocks and sand. A brief video of the collapse posted on the Beijing Times website showed a massive wall of reddish dirt or sand rushing down a slope onto mining vehicles below.

A subsequent landslide five hours later halted rescue efforts, which resumed on Thursday.

According to the official Xinhua News Agency, approximately 900 rescuers equipped with heavy equipment were on the scene. They were seen searching for miners with heavy machinery, shovels, and rescue dogs.

President Xi Jinping of China has called for a "all-out" search-and-rescue operation.

On Friday, security was tight at a checkpoint between Inner Mongolia and the neighboring region of Ningxia, with two police officers in yellow vests inspecting vehicles attempting to pass through what one of them described as a "restricted" area.

Some trucks were turned away, but others, including an emergency services vehicle driving at high speeds with its siren blaring and a truck carrying rescue supplies, were allowed in. The checkpoint appeared to be quieter than it had been the day before.

According to the news website The Paper, the mine's operator, Inner Mongolia Xinjing Coal Industry Co. Ltd., was fined last year for a variety of safety violations, including insecure routes, unsafe storage of volatile materials, and a lack of safety training.

Inner Mongolia is a key region for coal, mineral, and rare earth mining, which critics claim has ravaged the region's landscape of mountains, grassy steppes, and deserts.

China relies heavily on coal for power generation, but it has attempted to reduce the number of fatal mine accidents by emphasizing safety and closing smaller operations that lacked the necessary equipment.