A fire that trapped 28 workers at a Waihi mine for several hours yesterday continues to burn.

Mining company Newmont's Waihi mines are closed today, and investigations are underway after a fire threatened the lives of the workers and sparked a seven-hour rescue effort.

The drama began deep inside Newmont Trio mine, after the driver of a 35-tonne Kohmatsu truck noticed smoke coming from underneath the bonnet about 5am yesterday.

It sparked a huge rescue operation and saw workers hunkering down in three separate, underground rescue chambers until rescue teams reached them.

Newmont Waihi Gold spokesman Kit Wilson said as of 8am today the fire was still "smouldering".

He said investigators would not go down to look at the truck until it was completely cool.

"We will now just leave it to burn out completely, and that's partly because everyone is now out safely and due to it being a hard rock mine, there is nothing down there that would cause the fire to spread.

"There is also the potential though for the tyres on the truck to explode."

Wilson said because it was the first underground fire Newmont had dealt with, the company had consulted with overseas experts over how long it could take for a fire to burn out.

"We've been told 24-49 hours is normal for the vehicle to completely burn out and cool."

Once it had cooled, investigators would be sent down with thermal imaging binoculars.

Glen Grindlay, Newmont's general manager of operations, said staff who were underground at the time of the fire would be interviewed.

"The investigation is in an early stage and we need to let it run its course to find out what happened. But what we can say is that in six years of underground mining in Waihi this is the first incident of this type we have had. And what we do know is that all of our guys got out safely. Our people, our systems, our equipment and our training all worked as they should have worked.

"We are guided not just by New Zealand mine safety regulations, but are also heavily influenced by the regulations adhered to by our operations in Australia," he said.

Both Newmont and the Ministry of Business, Innovation and Employment's High Hazards Unit were investigating the incident.

Grindlay said underground mine operations were likely to reopen "within days, not weeks" but that would depend on how long the investigations took.

THE RESCUE

Grindlay said all miners were safely evacuated just before noon yesterday.

All but one miner, who was treated for smoke inhalation, escaped uninjured.

Despite New Zealand's sad history of mining incidents including the November 2010 tragedy at Pike River on the South Island's West Coast which claimed 29 lives, Grindlay said there was never any risk of an explosion at Waihi due to the nature of the hard rock gold mine.

All miners safely got to the underground rescue chambers - which are equipped with supplies including water and up to 55 hours of oxygen.

Underground manager Charlie Gawith said although it was a "really nice" feeling once the men were back up to the surface, “it was very stressful".

"You have got people in the refuge chamber underground. When you are driving to work you obviously have been informed of the incident and until you get to work and find out exactly where the incident is, and everyone is accounted for, it's quite a stressful time.”

Staff had been offered counselling, as some could be hesitant to return back underground.

Colleagues spoken to at a hotel wouldn't comment on specifics but said the whole rescue operation went well.

The partner of one of the men involved in the rescue effort said it was worrying.

“While it wasn't too bad for me, hearing it I did think of the other families.”

She said it could be quite nerve-racking having a loved one work in the mines, especially when things like this occurred.

Gawith said all the men had trained for events such as this. He said the driver of the truck which caught fire was quick to get in contact by radio, so the message that it was real and not a drill spread quickly.

Gawith said the injured man treated for smoke inhalation was now recovering.

Three Newmont Waihi Gold Mines Rescue Teams had helped with the evacuation. NZ Mines Rescue and Solid Energy had also offered assistance.

A miner's family member said he had been "impressed" with the way the rescue operation had unfolded.

Mines Rescue members reacted swiftly to the incident and the entire operation had "gone like clockwork".

- Additional reporting by Nicola Brennan-Tupara and Maryanne Twentyman

- © Fairfax NZ News