A third, more sophisticated robot is being readied to be sent into the Pike River Coal mine.
Two robots have been in the mine since Tuesday, one of which found a miner's helmut with its light still burning.
The third robot arrived from Western Australia on Wednesday morning.
Superintendent Gary Knowles describes the robot as a 'big beast'.
It will be tested and its capability determined before it is used.
A fourth robot is en route from the United States and is being flown courtesy of Air New Zealand and then by the Royal New Zealand Air Force to the West Coast.
It is due to arrive on Thursday morning.
The mine company says the robots have picked up bits of debris but nothing of any significance apart from the helmet.