At least six people were reported to be killed after parts of a mountain glacier collapsed in the Italian Alps on Sunday amid record high temperatures, local authorities said.

"Rescue operations are in progress following a large ice avalanche involving excursionists," the Trento provincial government said, adding that there was likely to be a "heavy toll" of injuries or deaths.

The avalanche took place on the Marmolada, a mountain of more than 3,300 meters in the Dolomite range in the eastern part of the Italian Alps, between the regions of Trento and Veneto.

A large chunk of Alpine glacier broke loose and slid down a mountainside, sending ice, snow and rock slamming into hikers on a popular trail on the peak.

The injured have been taken to nearby hospitals in the towns of Belluno, Treviso, Trento and Bolzano, said the president of Veneto, Luca Zaia.

Italian RAI state television said the fatalities numbered six, but that death toll couldn't immediately be confirmed. It wasn't immediately known how many hikers might be missing.

The National Alpine and Cave Rescue Corps tweeted that the search of the involved area of Marmolada peak involved at least five helicopters and rescue dogs.

It wasn't immediately clear what caused the section of ice to break away and rush down the peak's slope. But the intense heat wave gripping Italy since late June could be a factor, Walter Milan, an Alpine rescue service spokesperson told RAI state TV.

"The heat is unusual,'' Milan said, noting that temperatures in recent days on the peak had topped 10 degrees Celsius (50 degrees Fahrenheit). "That's extreme heat" for the peak, Milan said. "Clearly it's something abnormal."