The Defence Force has sent another bomb disposal robot to help at the Pike River coal mine near Greymouth, after the first one was knocked out by a waterfall.
Twenty-nine miners are missing in the mine, 50km north east of Greymouth, following an explosion on Friday afternoon.
The first Defence Force robot was sent down the mine this morning but failed just 550m in.
Defence Minister Wayne Mapp said the robots were bomb disposal machines and not designed for work in underground mines.
"It can operate in rain, but in this instance it was effectively hit by a waterfall and that knocked it out."
A second robot was sent by helicopter from Wellington.
Dr Mapp said there was more water in the mine than expected.
The first robot was carrying an additional two batteries, gas detection equipment and four cameras.
Further adaptations would need to be made before the second robot went into the mine, Dr Mapp said.
A specialist mine rescue robot was expected to arrive from Australia or the United States. The Defence Force would transport that robot from Auckland International Airport to Greymouth in a Hercules, he said.
Tasman Area Police Commander Superintendent Gary Knowles said today that as time went on, hopes of finding the miners alive were fading.
He briefed their families this morning on the latest situation regarding the planned rescue.
"I can tell you they are extremely frustrated and I can understand their frustration in relation to the time it has taken effecting a type of rescue, but as I have said safety is paramount to me."
It was considered too dangerous still to send in rescue teams, he said.
"Experts still tell us that the levels of toxicity and air underground are still too unstable to send rescue teams in.
"They do fluctuate depending on the biometric conditions...but at the end of the day safety is paramount in relation to sending teams in.
"We are planning for all possible outcomes we continue to plan and we will keep planning.
"This is a very serious situation and the longer it goes on, hopes fade and we have to be realistic.
"We are dependent on expert evidence to tell us daily what stage we are at so we can advance our rescue operation."
A member of the crew drilling a hole into the mine had been injured, Mr Knowles told a press conference.
"Originally, we thought he had some type of break to his leg, but it is just a sprain and that probably gives you some sort of idea of the nature of the crew and the conditions they are working under.
"This is extreme dense bush and these guys are working 24 hours a day and giving it their best shot so our sympathies are with him."
The hole should be completed this afternoon and listening devices would then be inserted into the mine.
The robot entered the tunnel about 6am today and Mr Knowles said he was told at 8am it had failed.
It was still inside the tunnel and would no longer be used.
"We have been in contact with our colleagues in America in effort to bring an advanced robot from there and we are negotiating with Western Australia to bring in an advanced robot from there."
He said police were liaising with the NZ air force in an effort to have a Hercules bring that to New Zealand.
