Authorities have been racing to dig out 22 miners trapped underground in the partially built gold mine in the city of Qixia in Shandong Province, since the explosion blocked their exit on January 10.

The rescuers set free two workers on Sunday, bringing the number of rescued miners to 11, the state-run Xinhua news agency reported.

The first miner was rescued from the mine in the morning. The worker, said to be in "extremely weak condition", was rushed to the hospital for treatment, the report said.

Currently, 633 people and 407 equipment are at the site for rescue operations.

Before Sunday, rescuers had established contact with only 10 of the miners, who were in good physical and psychological condition. Another is believed to have been dead, the report said, adding the deceased worker had been in a coma.

Efforts have been underway to reach the workers since the blast occurred about 240 meters from the mine's entrance, but Chinese officials said on Thursday it could take 15 days to drill through 70 tons of debris trapping many of the miners.

Food, medical supplies, blankets, and batches of nutrient solution have been passed down a shaft to the 10 workers who have been located, Xinhua reported.

According to state media, rescue teams are hoping to pull the miners out through a 711-millimeter diameter passage. By noon on Thursday, rescuers had drilled 18 meters into the mineshaft but heavy debris could slow efforts.

Concern has been growing for the uncontacted miners. Some of the workers in the chamber are trying to help rescuers locate their missing colleagues by using laser pointers and loudspeakers, but they have received no response.

Rescuers have also drilled smaller channels into other sections of the mine and are lowering nutrient solutions and other means to detect breathing or movement, but no signs of life have been encountered.

Rescue workers are reported to have first heard knocking sounds from those trapped on January 17, followed by pulling on iron ropes, CNN reported, adding that on Monday miners were able to get a note to rescuers.

A Xinhua report quoted the note as saying: "We are heavily exhausted and in urgent need of stomach medicine, painkillers, medical tape, external anti-inflammatory drugs, and three people have high blood pressure."

Explosions and deaths are not uncommon in Chinese mines. In September, at least 16 workers in southwestern China died after they were trapped underground in a coal mine and exposed to unsafe levels of carbon monoxide.

And in 2016, dozens of workers were confirmed dead after a gas explosion at a coal mine in the city of Chongqing.