A major operation to rescue 10 trapped Mexican coal miners is approaching a crucial moment, President Andres Manuel Lopez Obrador said, raising the hopes of desperate relatives.
"Today is a decisive day because, according to the experts, we'll know if it's possible for the divers to enter safely," he tweeted.
More than 300 soldiers and other personnel, including six military scuba divers, have joined the rescue effort in the northern state of Coahuila, the government said.
Five workers managed to escape from the crudely constructed mine in the initial aftermath of the accident on Wednesday, but since then no survivors have been found.
The focus has been on pumping out water from the mine in Agujita in the municipality of Sabinas to make it safe enough to enter.
Authorities said that the three mine shafts descended 60 meters and the floodwater inside was reported to be 30 meters deep.
"The main problem is the flood, although the pumping equipment is sufficient," said Mr Lopez Obrador.
Coahuila's state government said the miners had been carrying out excavation work when they hit an adjoining area full of water.
Experts detected a leak coming from nearby mines and aim to find its exact location so they can stop water flowing into the area where the workers are trapped, Coahuila's labor secretary, Nazira Zogbi, said.
A French company has provided equipment to assist in the task, she said, without naming the firm.
The arrival of more powerful pumping equipment was also a reason for optimism, Ms Zogbi added.
"Major progress has been made. It looks like we'll have better news," she said.
Water was seen flowing from the mine through drainage channels, lifting the hopes of relatives who spent a third night waiting anxiously for news.
"The last two days we didn't see any progress with the water, but now we see that a lot of water has come out," Elva Hernandez, mother-in-law of one of the trapped workers, told AFP.
"We're still hoping that they're in a higher part (of the mine), although there's too much water... but we trust in God," the 71-year-old added.
Coahuila, Mexico's main coal-producing region, has seen a series of fatal mining accidents over the years.
Last year, seven miners died when they were trapped in the region.
The worst accident was an explosion that claimed 65 lives at the Pasta de Conchos mine in 2006.
Only two bodies were retrieved after that tragedy.
Miners and their relatives painted a picture of a precarious profession fraught with risks due to lax safety standards.
"When everything's fine, you don't think about the danger, but when things happen you think about quitting," said Luis Armando Ontiveros.
However, looking for a new job does not seem like a viable option for the 48-year-old, whose father taught him to dig for coal at an early age.
The father-of-three said he needed the monthly salary equivalent to about $500 to pay for his children's education so they do not have to follow in his footsteps.