Visitors experience the chilly world of the country's biggest ice cave in Ningwu county, Shanxi province.[Photo by Wei Xiaohao/China Daily]

China's biggest ice cave, located in Shanxi province, continues to accumulate ice, according to local sources.

The cave, in the Luya mountain in Ningwu county, Xinzhou city, is connected to the Fenhe River, which is believed to be the water source, said Du Erping of the Luya scenic area's management office.

The cave is more than 100 meters deep at an altitude of approximately 2,300 meters. It was formed around 3 million years ago.

It is open for visitors from April to October each year, with a maximum of 3,000 people allowed to enter daily.

The wooden ladders in the cave are cleaned twice a day to avoid a buildup of ice.

"Because the ice continues to form, the cave changes all the time," Du said.

Scientists are still researching how the cave formed.

"Such caves are normally found in extremely cold areas, such as Antarctica or Siberia. But Luya mountain is at a latitude similar to Lisbon, Portugal," Du said.

The cave is less that half-an-hour's drive from the head of the Fenhe River. Once, as an experiment, a haystack was placed at the bottom of the cave and it disappeared. It was found the next day in the river. The cave also has several gaps allowing wind to blow through. Workers block the gaps during the day for the sake of tourists, and unblock them at night, Du said.

In the past, villagers used ice from the cave for medicinal purposes. However, to protect the cave, ice removal is now banned.