Several hundred rescuers, including soldiers and military scuba divers, are taking part in efforts to save the miners missing since August 3 in the northern state of Coahuila.
"We have all the conditions to go down there... to search for and rescue" the miners, civil defense national coordinator Laura Velazquez said by video link during President Andres Manuel Lopez Obrador's morning news conference.
But as nightfall later approached, Velazquez sounded a more cautious note, telling reporters it was unclear when the search would begin.
A specialist military team had made several more descents into one of the vertical shafts of El Pinabete mine to remove wood and other debris blocking their way, she said.
But they had not yet reached the floor of the 60-meter (200-foot) deep shaft to access the main tunnels where the workers were believed to be trapped, Velazquez added.
"I cannot even tell you for sure when we're going to enter the galleries. There's no way," she said.
Earlier Defence Minister Luis Cresencio Sandoval said that the water level in one of the three shafts that rescuers would try to enter has been reduced to 70 centimeters (27 inches), from more than 30 meters initially.
The other two shafts still have 3.9 and 4.7 meters of water.
Authorities consider 1.5 meters to be an acceptable water level to gain access to the crudely constructed El Pinabete mine.
"In any case, we're going to continue pumping... The process is slow but we don't want to take any risks," said Velazquez.
Five miners managed to escape following the initial accident, in which workers carrying out excavation activities hit an adjoining area full of water, but there have been no signs of life from the others.
For an optimal experience, please
