The company, which is believed to be interested in acquiring the Pike River mine, has been the focus of attention because 49% of its shares have been earmarked for privatisation by the newly-elected Key government.

“Solid Energy says its internet system was hacked overnight,” it said in a statement. “It has addressed the issue.

“The company adds that this is criminal activity under the Crimes Act and it has referred the matter to the police.”

Visitors to its website on Friday morning were redirected to another site, an address for "stolenenergy", which played a video about the possibility of lignite mining.

The incident highlights lack of security and safety at the company’s operations, which according to some have been questionable.

In August it announced it managed a 6.1% higher annual coal production of 4 million tonnes, despite only resuming coal mining at its Spring Creek mine in New Zealand in May, more than 19 months after heating incidents closed the hydro mining operation.

Solid, which has indicated it would like to acquire the nearby Pike River mine from its receivers, said it had made a significant investment in infrastructure at Spring Creek to ensure it operated safely as it announced the higher annual coal production figures, which were driven mainly by strong performance at its Stockton mine.

But safety incidents have continued to dog Spring Creek, with four since late April, including a frictional ignition event revealed by Solid Energy chief executive officer Don Elder during the Pike River Royal Commission hearings.

Solid previously announced there was a small fire on a load haul dump as it drove out of the mine on the evening of April 29.

The other incidents included a high voltage cable flash from a shuttle car underground on May 6, and a similar flash incident from a continuous miner on June 19.

But the most serious incident raised by Nigel Hampton, lawyer for the country’s mining union, the EPMU, was the frictional ignition incident on June 29.

Elder said the flame underground was described as 6 feet high and 4ft wide and was caused by a McConnell Dowell operator who had been cutting stone.

A major investigation was underway into that incident but the “vehicle” (probably a continuous miner) involved was deemed to be compliant from the company’s preliminary findings, he said.

“But the water sprays may not have been adequately functioning at the time, which may well have been because they were clogged, I don't know, and that’s what our investigation is intended to find out,” Elder said.