Police said the chopper came down near the Campo Felice resort during a mission to evacuate an injured skier.
"The area where it came down is hard to access at the best of times, and thick fog is making it even more difficult," a police spokesman told AFP.
"Several teams are trying to get there."
The helicopter issued a crash signal and the police had received reports of a loud explosion being heard, the spokesman said.
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It is a small resort popular with day-trippers from Rome, which is only 120 kilometres (75 miles) east of it.
The resort is at 710 metres (2,330 feet) altitude but the ski area goes up to just over 2,000 metres.
Police said there was no link to the recent seismic activity or the avalanche.
The accident happened as firefighters, mountain police and other emergency services are grappling with the aftermath of the earthquakes, the heaviest snowfalls experienced in decades and the avalanche that swamped the Hotel Rigopiano last week.
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