The pass separates Fujian and Jiangxi provinces. The water stored in buckets had a thick layer of ice, and the tap-water pipes were sometimes frozen stiff.

Li Hong, head of the pass, had to break the ice and run the taps before he stepped out for inspection.

Normally, the cold spell will last until mid-February.

Tongmuguan is one of the highest checkpoints in Fujian and plays a key role in crucial ecological protection tasks, such as forest fire prevention and resource conservation.

Li and several of his colleagues have to work in 24-hour shifts and often stand in the bitter cold.

Whenever vehicle horns blow, the personnel on duty take turns to man the checkpoint.

Facing the biting north wind, they signal the passing vehicles to stop for inspection and registration.

"We need to ascertain if they are carrying any contraband items, such as wood and wildlife," Li says, adding that they need to remove their gloves and touch the items with their bare hands to conduct a full inspection.

In addition to guarding the pass, Li and his colleagues also have to tour the surrounding forest.

"When encountering hikers entering restricted areas, we must immediately intervene and persuade them to turn back," Li says.

If hikers suffer from frostbite or injury, they also have to carry out first aid.

Although the work in the deep recesses of the mountain is arduous, Li says the best reward comes when he helps endangered animals.

According to local authorities, the natural reserve has had no fire or poaching incidents in the past four decades.

A 90-minute drive from Tongmuguan, in the direction of the downtown area, the Wuyishan national park's intelligent management center keeps track of the real-time entry and exit of tourists, the hydrological and atmospheric conditions, as well as the movement of patrol and protection personnel.

"This allows for dynamic supervision of resource protection, emergency management and environmental capacity warnings at the national park," says Fan Zhiwei, a staff member with the park.

The application of evolving technology has also made things easier for workers on the front line.

Forest rancher Zhang Quan says he now just has to put the coordinates of a specific location into his tablet computer and the real-time satellite images and historical satellite images of that area will be presented.

"Through comparison, we can identify whether there have been changes in the ecological environment, greatly enhancing our efficiency," Zhang says.

In 2023, the national park designed 4,970 patrol routes where patrols have cumulatively reached 33,830 km.

The park has also introduced drone patrols in key protected areas and unmanned zones that are difficult for personnel to reach.