Rescuers have found body parts and equipment as they search for hikers missing following a powerful avalanche that killed at least seven people.

Officials initially feared 13 hikers were still missing on the Marmolada glacier, east of Bolzano in the Dolomite mountains, but the province of Trento reduced the number of people unaccounted for to five after eight others checked in with authorities.

Rain hampered the search on Monday, but sunny weather on Tuesday allowed helicopters to bring more rescue teams up to the site, even as hopes dimmed of finding anyone alive.

A huge chunk of the glacier fell off on Sunday, sparking an avalanche that sent torrents of ice, rock and debris ploughing down the mountainside onto unsuspecting hikers below.

At least seven people were killed, officials said.

“We have to be clear, finding someone alive with this type of event is a very remote possibility, very remote, because the mechanical action of this type of avalanche has a very big impact on people,” said Alex Barattin of the Alpine Rescue Service.

Nicola Casagli, a geologist and avalanche expert at Florence University, said the impact of the glacier collapse on the hikers was greater than a mere snow avalanche and would have taken them completely by surprise.

“These types of events, which are ice and debris avalanches, are impulsive, rapid, unpredictable phenomena, reaching very high speeds and involving large masses,” he said.

“And there is no chance of getting to safety or perceiving the problem in advance, because by the time you perceive it, you’ve already been hit.”

Associated Press photos, taken during a helicopter survey of the site, showed a gaping hole in the glacier.

The terrain is still so unstable that rescue crews stayed off to the side and used drones to try to find any survivors or signs of life while helicopters searched overhead, some using equipment to detect mobile phone pings.

Two rescuers remained on site overnight, and were joined by more rescuers on Tuesday morning.

Maurizio Dellantonio, national president of the Alpine Rescue Service, said teams had found body parts, hiking equipment and clothing on the surface of the debris, evidence of the avalanche’s powerful impact on the hikers.

“We have recovered so many fragments over the last two days. They are very painful for those who pick them up. And then for those who have to analyse them,” he said.

“Personally I can only think that what we found on the surface will be the same that we will find underneath, when the ice will melt, or by digging, if there is a chance.”

Officials closed all access routes and chair lifts to the glacier for hikers, fearing continued instability and the potential that more chunks of ice might detach.

Premier Mario Draghi, who visited the rescue base in Canazei on Monday, acknowledged avalanches are unpredictable but that the tragedy “certainly depends on the deterioration of the climate situation”.

Italy is in the midst of an early summer heatwave, coupled with the worst drought in northern Italy in 70 years. Experts say there was unusually little snowfall during the winter, exposing the glaciers of the Italian Alps more to the summer heat and melting.

“We are thus in the worst conditions for a detachment of this kind, when there’s so much heat and so much water running at the base,” said Renato Colucci from the Institute of Polar Sciences of the state-run Council for National Research (CNR).

“We aren’t yet able to understand if it was a deep or superficial detachment, but the size of it seems very big, judging from the preliminary images and information received.”

The CNR has estimated that the Marmolada glacier could disappear entirely in the next 25-30 years if current climatic trends continue, given that it lost 30% of its volume and 22% of its area from 2004-2015.

Casagli said what happened on the Marmolada was unusual, but said such destructive avalanches will become more frequent as global temperatures rise.

“The fact that it happened in a scorching summer with abnormal temperatures must be a wake-up call to understand that these phenomena, while rare, are possible,” he told reporters. “If we don’t take decisive measures to counter the effects of climate change, they will become more and more frequent.”