It has been five days since an explosion tore through a gold mine under construction in eastern China's Shandong Province, and 22 miners are still trapped underground.
Nearly 400 rescue workers have been working around the clock in search and rescue operations, supported by four drilling machines on site.
But so far, there have been no signs of life.
Local authorities said a line had been fed beneath the surface to a depth of nearly 400 meters to ventilate the shaft and remove any dangerous gases or smoke.
Rescuers were still unable to make contact with the miners because the communication signal was damaged in the blast. But they managed to place monitoring equipment at a depth of 370 meters to detect if there was any sound from the trapped workers.
An expert from the rescue team said the biggest challenge they faced was cleaning up obstacles in the shaft.
"Due to the impact of the explosion, the structure in the shaft has been severely damaged, and much of the equipment previously installed in the shaft has fallen off and is stuck inside. The steel ropes of the pipeline are tangled up together. All of this is making it very difficult for the rescue operation, and it's slowing down progress," said Xiu Guolin, director of security at Shandong Gold Group.
Local authorities said concentrations of carbon monoxide, oxygen and temperature levels at a depth of 310 meters were normal.
The gold mine is owned by the Shandong Wucailong Investment Company, which has been criticized for a 30-hour delay in reporting the accident.
Chinese law and regulations are clear that accidents of this nature need to be reported to the local government within one hour.
"Those responsible at the company have been placed under investigation and will be held accountable in accordance with the law. Shandong Province has established a specific team to investigate the cause of the explosion and the company involved. And the results of the investigation will be announced to the public in a timely way," said Li Bo, deputy mayor of Yantai City.