GREYMOUTH, New Zealand — Rescue efforts got a boost Wednesday with a drill breakthrough at the New Zealand coal mine where 29 miners were caught in a methane-fueled explosion last Friday. Nothing has been heard from the miners since.

The drill hole 530 feet (162-meters) deep into the mine broke through the mine’s main tunnel roof, causing “hot air and gases to rush up,” Pike River Coal Ltd. chairman John Dow said.

Rescuers immediately began sampling gas from the hole, which is located near where some miners were working when the blast happened on Friday.

“The air from the (bore) hole was extremely high in carbon dioxide, very high in methane and fairly low in oxygen,” Pike River Mine chief executive Peter Whittall said, adding that it is still too soon to allow rescuers access to the mine.

Pike River company chairman John Dow said the breakthrough deep into the mine would provide a much better understanding of “what the atmosphere is like in this part of the mine. It will be quite critical as to what happens next.” Rescuers plan to put a video camera down the hole to look for signs of the missing miners.

Earlier Wednesday a bomb disposal robot was restarted and sent further down the shaft to check the tunnel and toxic gas levels.

Police say the robot, which stalled after hitting water, has now gone two-thirds of a mile (a kilometer) into the mine to collect air samples and send back video. They have yet to release details of what it detected.

A second robot is on its way into the mine, police said.

Rescue controller, police superintendent Gary Knowles, said the air samples from the bore were “off the limit (and) the environment is currently unstable” in the mine.”

“It is not possible to send rescuers underground,” he said.