NZ Defence Minister Wayne Mapp defended the performance of the first robot, which remains stranded 550m into the main access tunnel.

“The robot is not actually designed for this purpose but can operate in rain, but [in] this instance was effectively hit by a waterfall which then knocked it out," he said according to the New Zealand Herald.

Grey District Mayor Tony Kokshoorn asked the publication why the robot did “not have a bit of Glad Wrap” over it when he expressed his disappointment.

Even though the mine is a hydro-mining operation that uses high-pressure water to cut the coal, it appears the risk assessments for the robot did not ensure it was waterproof.

The second robot will hopefully be more successful after it is given the go-ahead.

The idea of sending in a robot has already received scientific criticism on the basis the machines are not flame proof or intrinsically safe.

Robots are yet to notch up any notable successes in underground mine search and recovery operations either.

With two spare arms, the second robot can also be fitted with a camera and devices to detect gas levels.

Using a robot will avoid losing lives as concerns remain that there could be secondary explosion in the mine.

Meanwhile, drilling of the second borehole is expected to be complete within hours.

At a planned length of 162m, the 15cm diameter hole will intercept a roadway roughly halfway between the mine’s pit bottom and the working areas where many of the missing miners are expected to be.

The hole will allow more gas samples to be taken to get a better idea of the atmosphere underground.

Fibre-optic cable will also be put down the hole to get first images underground since the Friday afternoon explosion.

Two Australians are missing out of the 29 unaccounted miners.