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Two NZ Defence Force robots entered the mine tunnel today, covering almost twice the ground as yesterday's attempt.

The first robot managed to travel about a kilometre, close to the point where Russell Smith was when Friday's blast occurred.

The Herald understands the second is about 800m into the tunnel.

Yesterday, one of the robots travelled 550m but malfunctioned following water damage. The robot was restarted this morning.

While the robots made progress, they would have to travel more than twice as far again to reach the tunnel network shown on the map.

Yesterday, Mr Whittall outlined where authorities believe the 29 men are trapped within the mine.

He described the main tunnel leading off to the right of the map as the "barrel of the a gun". This tunnel is about 2.5 kilometres in length.

Although he could not confirm exactly where in the mine the explosion occurred, he said it rocketed down the main shaft where it knocked Daniel Rockhouse off his loader.

He said Mr Rockhouse was in a small shaft off the main tunnel just to the right of the map's border when the blast hit.

Mr Whittall said that because Mr Rockhouse was not in the main tunnel "he was knocked over but not seriously injured".

Russell Smith was further up the tunnel "several hundred metres" towards the mine's entrance.

From the two men's escape, authorities know that the main shaft up to the point where Mr Rockhouse was found is clear of rubble of debris.

Mr Whittall said that air was currently flowing down the main tunnel and out of the ventilation shaft.

He said there are systems which work to keep fresh air flowing throughout the mine, but is unsure if these are operating.

Mr Whittall said the drill hole currently being bored is about halfway between the end of the entrance tunnel and the far end of the mine.

"We're expecting that this hole will be into a gassy environment," the Pike River chief executive said.

He said there is the expectation there will be gas in the area left of the ventilation shaft, though he could not confirm exactly where.

He said the location of the second place where they plan to drill is very close to where they believe the miners are.

"We don't know what information that would give us, we haven't started that hole yet.

"But we are starting to clear that area and ready to take the rig from one spot to another.

"We are also investigating a second rig to mobilise to that site. However, if the air is heavily concentrated in the first hole, [the second hole] may not give us more information from a gas point of view but that's something the rescue service will deal with," he said