Flames were last night shooting from the top of a 108m ventilation shaft at the Pike River coal mine - and only a couple of mountain peaks away a 43-year-old fire from the Strongman mine continues to billow smoke.

It has been 10 days since an explosion trapped 29 men underground at Pike River, and now a huge coal fire is burning inside the mine, hindering efforts to recover the men's bodies.

The fire is visible from a helicopter, belching smoke and flames from the wrecked top of a ventilation shaft which runs longer than a rugby field into the mountain. No flames were previously visible, even during the initial methane explosion.

Pike River chief executive Peter Whittall said the fire in the mine - which had been burning gas since at least a week ago - had begun burning coal after a fourth explosion.

It was hoped that loose coal dislodged during the four explosions was burning, he said.

That is preferable to the fire getting into the mine's walls of solid coal.

Such a fire would create vast amounts of heat and be difficult to extinguish.

Mr Whittall likened this situation to a coal range.

"The worst-case scenario is that the walls of the mine, which are coal, can burn. That's a lot harder to smother because it just sits there like when you shut a fire in overnight in the old coal ranges.

"They just sit there and virtually do nothing, then in the morning you open up the air and they start again."

Grey District Mayor Tony Kokshoorn said there was "total silence" from the families of the lost miners when they heard the latest update.

"They're totally subdued and they're desperate now," he said. "How long do they have to wait to get their loved ones out of there?"

Those running the recovery operation hope to put out the fire by starving it of oxygen. That could mean temporarily sealing the mine so no air can get in, or using a "GAG" jet engine brought from Australia to fill the mine with water vapour.

Authorities have not made clear which they prefer, but they say that either way, it could take several weeks before the fire went out even after it was starved of oxygen.

The length of time it took to kill the fire would indicate how much coal is burning and therefore whether the mine walls and the coal seam in the mountain are alight.

The Strongman mine, where 19 men died in 1967, continues to burn near Pike River, giving off plumes of smoke after 43 years.

Mr Whittall said it was unlikely Pike River would burn indefinitely in a similar way because unlike other mines in the area, it did not have cracks to let fresh air in.

The Strongman disaster - like the one at Pike River - was caused by a methane explosion.

Two bodies from the Strongman mine were never recovered.

The section of the mine where the blast occurred was sealed off, but the mine was reopened.

Police Inspector Mark Harrison, who is leading the recovery operation at Pike River, said the fire made it less likely that the bodies of the 29 men could be recovered intact.