New Zealand police on Tuesday announced a criminal investigation to probe how an eruption at the White Island volcano led to an estimated 13 deaths.

Police Deputy Commissioner John Tims said the terms of reference for the investigation will be determined in coming days, The New Zealand Herald reported

The announcement comes as attempts to recover the eight people on the island who are missing, presumed dead and likely to be covered in ash.

Police have confirmed five people were killed and another eight were missing presumed dead after New Zealand’s most active volcano exploded while tourists were exploring it on Monday afternoon.

Speaking before the investigation was announced, travel operator White Island Tours said it took safety responsibilities extremely seriously.

“We take our steer from (government geoscience agency) GNS, who send us a report telling us what the activity levels are if it’s deemed level two, which it was yesterday,” chairman Paul Quinn told TVNZ.

Of the 31 injured, 25 are in four regional burns units around the country. The six others will be transferred to burns units as soon as possible, according to health authorities.

Meanwhile, experts have warned that there was a 50 per cent chance of another eruption within 24 hours, The New Zealand Herald reported.

Prime Minister Jacinda Ardern said while speaking to media on Tuesday that “no signs of life have been seen at any point” after helicopters and aircraft took a number of aerial reconnaissance flights over the island since the eruption.