Chinese miners trapped underground for nine days are recovering strength after food and medical supplies were lowered to them, rescuers said Tuesday, as authorities raced to save the workers.

Some 22 workers were trapped at the Hushan mine near Yantai in east China's Shandong province after an explosion damaged the entrance.

One group of the miners managed to send a note attached to a metal wire which rescuers had dropped into the mine on Sunday after days without any signs of life.

The handwritten message said a dozen of them were alive, but surrounded by water and in need of urgent medical supplies.

Several were injured, the note said.

Map locating Qixia city in China's eastern Shandong province near where 22 miners have been trapped underground since January 10
Map locating Qixia city in China's eastern Shandong province near where 22 miners have been trapped underground since January 10 AFP / STAFF

Subsequent communication revealed 11 were in one location, 540 metres (1,750 feet) below the surface, with another -- apparently alone -- trapped a further 100 metres down.

The whereabouts and condition of the other 10 miners is still unknown.

Rescuers have already dug three channels and sent food, medicine, paper and pencils down thin shafts -- lifelines to the miners.

Rescuers on Tuesday said two miners who were "very weak" had regained their ability to walk, the official Xinhua news agency reported.

However, one of the miners is in a coma after being injured in the blast, state broadcaster CCTV said.

Rescuers have already dug three channels and sent food, medicine, paper and pencils down thin shafts
Rescuers have already dug three channels and sent food, medicine, paper and pencils down thin shafts AFP / -

The progress of the rescue has been slow, according to Chen Fei, a top city official.

"The surrounding rock near the ore body is mostly granite... that is very hard, resulting in slow progress of rescue," Chen told reporters on Monday evening.

"There is a lot of water in the shaft that may flow into the manway and pose a danger to the trapped workers."

Chen said the current food supply was only enough for two days.

Rescuers drilled three more channels on Tuesday, according to a rescue map published on the Yantai government's official twitter-like Weibo account.

A telephone connection has also been set up.

Footage from state broadcaster CCTV showed dozens of rescuers clearing the main return shaft, while cranes and a massive bore-hole drill was used to dig new rescue channels to reach the trapped miners.

Rescue teams lost precious time as it took more than a day for the accident to be reported, China Youth daily reported citing provincial authorities.

Both the local Communist Party secretary and mayor have been sacked over the 30-hour delay and an official investigation is underway to determine the cause of the explosion.

Mining accidents are common in China, where the industry has a poor safety record and regulations are often weakly enforced.

In December, 23 workers died after being stuck underground in the southwestern city of Chongqing, just months after 16 others died from carbon monoxide poisoning after being trapped underground at another coal mine in the city.

China Safety