Southwest China's Tibet Autonomous Region has banned visitors from passing through a state nature reserve to access other areas, as an environmental protection measure.

In a circular released Friday, the regional forestry bureau said that any crossing at the Changtang National Nature Reserve (CNNR) will be illegal. It specifically mentions that people should not pass through the CNNR to reach two other state nature reserves, one in Xinjiang and another in Qinghai.

The CNNR covers six counties in Tibet's Nagqu Prefecture. With an area of 298,000 square km and an average altitude of 5,000 meters, it is China's biggest and highest reserve. The area is a wildlife paradise, and home to a variety of wildlife species and numerous lakes.

The circular called on tourists, adventure enthusiasts and tourism agencies to comply with the reserve's laws and regulations to "protect the last pure land on earth."

Tibet has increased protection efforts at the CNNR. In 2015, the regional government established 73 management stations at the reserve and hired a total of 780 farmers and herdsmen to patrol, manage and protect the reserve at a cost of 300 million yuan (43 million dollars).