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Four drones from the national mapping agency are currently in the quake hit region in Ludian county. In the 24 hours since the disaster, they took hundreds of videos and images of some 60 square kilometres around the epicentre. This is greatly helping¹ rescuers plan ahead, to ensure timely rescue and relief work.

This aerial photo taken on Aug. 4, 2014 shows buildings toppled down by a 6.5-magnitude earthquake at the quake's epicenter in Longtoushan Town under Ludian County of Zhaotong, southwest China's Yunnan Province. (Xinhua/Xue Yubin)

A whole and clear picture of the destruction the disaster has brought. These videos, taken within 24 hours of the quake, show what rescuers were up against.

"Barrier lakes are a huge danger. Other factors that may hamper² the rescue efforts are mudslides and traffic jams," Luo Jianjun, deputy director of National Geomatics Center, said.

Water levels in barrier lakes, which were formed by mudslides pouring into rivers, have been rising fast since day one. That has put villages further downstream in danger. Experts are analyzing³ pictures and videos by comparing them with geological images from last year.

"The water level in this lake has risen by 30 metres in just one day. This is very dangerous. As we can see from this animated⁴ video, this is the normal water level. And in this video, it is already three times larger," Luo said.

The images also show at least eight major sites where landslides⁵ have occured. All are located on roads leading to the epicenter. As a result, traffic jams have hampered⁶ the flow of rescuers and relief materials.

"The yellow ones are serious mudslides. We can see this whole road has been interrupted. It’s quite difficult to clear it. This is a rescue team, which is stuck on the road," Luo said.

Experts have asked people living downstream from the rivers to evacuate⁷, since the barrier lakes can burst any time. Meanwhile, these drones will continue with their vital work to prevent any more loss of lives.