(CNN) -- A second robot has arrived at the site of a coal mine in New Zealand where an explosion trapped 29 workers underground, police said.
But police officials stressed that it remained too dangerous for human rescuers to go underground, and the situation at the mine was growing increasingly grim with each passing hour.
"The situation is bleak. It is grave. And you have to understand that the risk posed by a secondary explosion is real," Gary Knowles, superintendent of the Tasman Police District, told reporters Tuesday.
While teams are preparing for a rescue, he said, "the likeliness of this occurring is diminishing".
CNN
