A body of one of the three trapped miners has been found but rescuers are trying to reach the two others. The indentity of the dead miner isn't known at this stage.
Don Schofield, Chief Inspector of Industry for Workplace Standards Tasmania, said two senior officers were at the mine site.
But he warned any investigation would take "some time" because of the complex geotechnical aspects involved.
Investigators will initially focus on the rockfall that followed a seismic movement on Tuesday night leaving miners Todd Russell, Larry Knight and Brant Webb trapped nearly a kilometre underground.
"Grave fears"
Beaconsfield Gold Mine manager Matthew Gill told reporters at the scene that a body was found at 7.22am (AEST).
"One body was found during the rescue process at the Beaconsfield mine site. It is currently not known who the deceased is," Mr Gill said.
"The fate of the other trapped miners is not known but grave fears are held."
The mining company could face a $150,000 maximum penalty if any breach of the Workplace Health and Safety Act is identified.
Earthquake blamed
Fourteen other miners working underground at the same time made it to a safety chamber and escaped unscathed.
The 1,000-strong community of Beaconsfield, 40 kilometres north-west of the city of Launceston, has spent an anxious night waiting for news.
Earlier West Tamar mayor Barry Easther told Channel Nine: "They are making progress ... I know they have been working very hard overnight to try and get to the area where the trapped miners are."
He said the families, who are being cared for by counsellors, are desperate for news.
Rescue equipment
An earthmover, equipped with cameras and remotely-controlled, was to be sent into the mine to try to dig its way through to the trapped men.
Mine manager Matthew Gill said that grave fears were held for the men, but one ray of hope was that the mine's ventilation system was still working and water supplies were not a concern.
Mr Easther said the men had gone missing in a "very delicate area of the mine", and if they survived the initial rock fall it was possible they were still alive. "My advice from the mining company is that there is oxygen down there," he said.
Mr Easther also said it was hoped the incident did not force the permanent closure of the mine, as opinions are split over whether the rock fall was an act of God or caused by mining in unstable conditions.
"It's a very important part of the community," Mr Easther said of the mine, the town's major employer.
"The employment here is good, the economic benefit to our local community is good too, we certainly hope that measures will be found to enable this mine to continue in operation."
Union demand inquiry
Australian Workers Union national vice president Paul Howes said union officials would meet Tasmanian Deputy Premier Bryan Green to demand a full inquiry into the accident
He said AWU members would not return to the site until it was deemed safe. "We won't be allowing any of our members to put their lives at risk for a couple of ounces of gold anymore," he said.
Mr Howes said he was satisfied with rescue efforts but still had concerns about the cause of the rock fall. A minor earthquake that measured 2.1 on the Richter scale has been blamed for the rock fall.
Asked if mining caused seismic activity, he said: "In our belief it does, no doubt".