The so-called "rat-hole" diggers — men who risk their lives working in illegal mines — were lost on December 13 after water gushed in from a nearby river, in the remote northeastern state of Meghalaya.
Dozens of emergency workers have since been racing against time to rescue the miners from a 106-meter shaft.
There has been no contact with the workers but their families are clinging to hopes that they are in an air pocket.
Rescue chief S.K. Shastri told AFP nothing has been heard from the miners, but that "in such cases we always presume they are alive."
Engineers are struggling with ineffective machinery that cannot cope with the deluge in the pit.
"The water level hasn't gone down an inch -- it increased after it rained," Shastri said. "The two 25 horsepower pumps were ineffective. We need up to 12 100 horsepower pumps to drain out water."
The river is also still pouring into the shaft making it dangerous to send down divers, according to Shastri, who added that the collapse of the tunnel walls could have caused leaks into other mines.
A miner who survived the flooding told reporters five men escaped as water burst into the pit.
"I was about five feet away from the ground that morning and on my way up, when I suddenly felt a lot of air and then saw water," the 21-year-old said.
Mining was banned in the mineral-rich state by a federal court in 2014 after local communities said it was polluting water bodies. But the practice continues with locals illegally extracting coal using dangerous "rat hole" mines.
This involves digging into the side of hills and then burrowing horizontal tunnels to reach a coal seam.
At least 15 miners were killed after they were trapped in another flooded rat-hole mine in Meghalaya in 2012. Their bodies were never recovered.