Rescue teams have resumed their search for 13 climbers who have been missing since part of a glacier gave way high in the Italian Alps on Sunday, killing at least seven people.

Hope of finding survivors is fading more than 36 hours after a disaster that has fuelled concerns about the impact of climate change on the mountains.

Three people from the Czech Republic were among those unaccounted for.

Sunday's avalanche took place on the Marmolada, which at more than 3,300 metres is the highest peak in the Dolomites, a range in the eastern Italian Alps straddling the regions of Trento and Veneto.

An aerial view taken today of the collapsed glacier

With the peak still unstable, rescuers have been using drones and helicopters to look for victims or to try to locate them through their mobile phone signals.

Italian media said those confirmed to have been killed included Davide Miotti, a 51-year-old local alpine guide who ran a sports shop in the area.

Much of Italy has been baking in an early-summer heatwave and scientists said climate change was making previously stable glaciers more difficult to predict.

View of the glacier from the valley below it today

Italian Prime Minister Mario Draghi said the disaster was linked to environmental factors.

"The government must think about what has happened and take steps to ensure that what happened is unlikely to do so again or can even be avoided," he said during a visit to the site yesterday.

Italy has declared a state of emergency for areas including Veneto surrounding the river Po.

Land beside the waterway accounts for roughly a third of the country's agricultural production and is suffering its worst drought for 70 years.