All 29 miners trapped underground following an explosion last week in a New Zealand mine are dead, the official in charge of the rescue attempt said Wednesday. "There was another massive explosion underground, and based on that explosion, no one survived," Gary Knowles, superintendent of Tasman Police Command, told reporters. "We're now going to recovery mode." Knowles said he was at the mine when the second explosion occurred on Wednesday afternoon. "The blast was horrific -- just as severe as the first blast," he said. Knowles said he did not know and would not speculate on the cause of the blast. During the rescue attempt, air released from drilling into the mine contained high levels of carbon monoxide and methane but little oxygen, according to police officials. The CEO of Pike River Coal, Peter Whittall, told reporters Wednesday he did not know where either of the blasts occurred in the mine, but said "the mine would have been filling up with gas. It would have already had gas in it." When asked about the possibility of survival, Whittall said, "I'm advised that on the strength of this, and the evidence of it, it's extremely unlikely." Map: New Zealand coal mine RELATED TOPICS * Mining Accidents and Disasters * New Zealand Whittall said "we want our boys back, and we want to get them out." "I still want them back. And their families want them back. And we'll be doing everything we can to make that happen," he said. But he added, "We can't still go back into an unsafe mine ... the gas will still be coming out of the coal." The 29 men, ages 17 to 62, had been missing since Friday, when an explosion ripped through the Greymouth mine. Most of the miners are from New Zealand, but the group also includes Scotlanders and South Africans. Authorities said the two camera-bearing military robots sent into the mine had found a worker's helmet with its light still on but no sign of life. The helmet, police said, was dropped by one of the two miners who escaped the original explosion. One of the units reached a "fresh air base" and found nobody there, he said. The missing men were believed to have been spread throughout the mine, with perhaps half trapped in one area. Whittall and Knowles reiterated that potentially explosive gases in the collapsed mine have rendered a rescue attempt unsafe so far. "It's just too dangerous. You can't put the lives of the guys going underground at risk," Whittall said. Late Tuesday, officials showed family members and reporters a closed-circuit television video of the mine's entrance during Friday's blast. The minute-long video shows dust flying and a white screen flapping back and forth before it is blown out of the tunnel. The video "showed that the blast was quite large and went on for a long time," Whittall said. He said that the "sobering" video showed a site at least 2.5 kilometers (1.6 miles) away from the blast. Officials decided to play it for family members and reporters to illustrate "how dangerous it would be to re-enter the mine," he said. Source: CNN