But police officials stressed that it still remained too dangerous for human rescuers to go underground, and the situation at the mine was growing increasingly grim with each passing hour. 

No one has heard from the men -- ages 17 to 62 -- since the explosion. Workers are trying to drill a hole down into the mine to contact them, but a potentially explosive mix of gases inside has kept rescuers from entering. 

Earlier on November 23, police said the first military-operated robot dispatched to search for signs of life in the mine had broken down about 550 meters (1,800 feet) inside the tunnel. 

A second New Zealand military robot arrived later in the day, and negotiations to get additional robots from America and Australia are underway. 

Officials said rescuers are still working on a 6-inch-wide bore hole, which will allow rescue workers to collect gas samples and other data once it breaks through. Drill crews had bored about 145 meters (476 feet) into the earth on the evening of November 23 (local time). 

Workers expect to put laser imaging gear down the hole so they can see what it looks like inside the mine, which is located on the west coast of southern New Zealand, between Greymouth and Reefton.