Most of the 29 dead are thought to lie behind a large rockfall, more than 2 kilometres in. Pike River hopes to install a special grout close to that fall.
Four robots with cameras used in the wake of the November disaster still remain in the mine and have provided footage up to a depth of 1600m. The only other images have been taken by cameras lowered down boreholes.
The juggernaut that survivor Russell Smith was driving at the time of the blast is located 1570m in.
"Past the 1600m point is unknown territory. There could be other rockfalls we don't know about, twisted metal and the possibility of bodies," Mr Ellis said.
"If this is the case while we are in the process of reclaiming the tunnel we will put up a temporary seal and police and forensics can safely walk into the mine," he said.
New Zealand contractors Webster Drilling and an Australian firm, Wilsons, will commence work in November. A six-inch hole is to be drilled from the surface, and foam - which will rapidly expands upwards - will be pumped into the tunnel, where it will set and seal. Although it has been used overseas, it has never been used in New Zealand.
Receiver Malcolm Hollis of PricewaterhouseCoopers said reclaiming the tunnel also made commercial sense.
"We are happy with the interest we have in the mine. There is international and local interest but that is confidential information. Intended parties will need to have a firm bid on the table at the end of the month - we will then have a far clearer picture of where parties are at."
Mines Rescue said last week it was prepared to start a proper 'reconnaissance' walk in up the tunnel using breathing apparatus. But Mr Ellis said no, due to safety concerns.
He wants to wait until the new grout is installed and the main tunnel reventilated closer to Christmas, so Mines Rescue can enter without breathing apparatus.
New Zealand Oil and Gas is spending $1.4 million in reclaiming the tunnel to 2.4km.
There are currently no firm plans for how to get past the rockfall into the main area of the mine.
