Rescuers have found body parts in the search for hikers missing after a powerful avalanche killed at least seven people in Italy.

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 to five after eight others checked in with authorities.

Rain hampered search efforts on Monday, but sunny weather on Tuesday allowed helicopters to transport more rescue teams to the site – though hopes of finding anyone alive were becoming increasingly scant.

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

Officials said at least seven people were killed.

“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.

Photos taken during a helicopter survey of the site showed a gaping hole in the glacier.

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

Two rescuers remained on the site overnight, though they 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 top of the debris, evidence of the avalanche’s powerful impact.

“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 have closed all access routes and chair lifts to the glacier for hikers over fears about continued instability and the potential more chunks of ice might detach.

Italy’s Prime Minister Mario Draghi, who visited the rescue base in Canazei on Monday, acknowledged avalanches are predictable but sid the tragedy “certainly depends on the deterioration of the climate situation”.

Italy is currently experiencing an early summer heatwave, along with the worst drought in the north in 70 years. Experts said there were unusually small amounts of snowfall during the winter, exposing the glaciers of the Italian Alps to the summer heat and melting.