The death toll from an avalanche that swamped an Italian mountain hotel rose to 15 Tuesday, with 14 still missing, as a nearby helicopter crash left six people dead and dealt another blow to a region reeling from earthquakes and the heaviest snowfall in decades.

The emergency response helicopter came down in thick fog near Campo Felice, a popular ski resort 120 kilometres (75 miles) east of Rome, during the evacuation of an injured skier.

There were reports of a loud explosion being heard.

"Rescue teams have reached the wreck of the helicopter and they found the bodies of the six deceased in the snow," a police spokesman told AFP.

Campo Felice, located at 710 metres (2,330 feet) altitude but with pistes up to just over 2,000 metres, is close to the epicentres of earthquakes that struck the region last Wednesday and were followed by the killer avalanche.

Police said there was no apparent link between the crash and the seismic activity or the avalanche.

But it came as firefighters and mountain police grappled with their aftermath.

A team of first responders who had been helping the rescue effort at the Hotel Rigopiano was dispatched to the helicopter crash site but would not have been able to get there before news of the deaths came.

The tally of bodies found in the ruins of the Rigopiano rose to 15 on the sixth day of an increasingly forlorn search through the snow-covered wreckage.

Eleven staff and guests survived the disaster, two men who we outside when the avalanche struck and nine people, including four children, who were found on Friday.

Rescuers have refused to give up hope of finding more people alive with morale amongst the exhausted rescuers having been boosted on Monday when three puppies were retrieved alive from under the rubble.

Italian authorities are investigating the chain of events leading to the avalanche to see if the tragedy could or should have been avoided.

A preliminary manslaughter investigation has been opened with the prosecutor in charge looking into whether environmental risks were properly taken into account during the construction and subsequent renovation of the hotel.

Events on the day of the disaster itself, when guests were unable to leave because of snow-blocked access roads, are also in the spotlight.

- Tunnelling into wreckage -

The local council had only one functioning road-clearance vehicle and had deployed it to reach isolated hamlets with elderly residents rather than clearing the road to the hotel.

A second snow plough had broken down earlier in the month and staff were awaiting authorisation to get a 25,000-euro ($26,800) repair done.

The hotel, a four-star spa facility where George Clooney once stayed, was built into a hillside at 1,200 metres altitude on the eastern slopes of Monte Gran Sasso. Campo Felice is on the other side of the near 3,000-metre peak that dominates the region.

The survivors pulled from the ruins on Friday were all treated for mild hypothermia, suggesting anyone still alive nearly four days later would have had to have found some way of keeping warm.

Rescuers have not ruled that out because they believe some rooms they are trying to reach by tunnelling through thick stone walls may be almost intact.

New routes have been dug into the rubble but progress remained painfully slow with the first responders often digging with their bare hands because of fears of masonry or snow slides.

The avalanche occurred three hours after the last of four magnitude five earthquakes shook the region in the space of four hours.

Police have calculated the force of the impact on the three-storey stone and wood structure as being equivalent to it being hit by 4,000 fully-loaded trucks.

The first funerals for the victims were held Tuesday.