Ten people were killed and 11 injured in a flash flood that filled a gorge in Italy's Pollino National Park following heavy rains on Monday, The Associated Press reported.

The victims were from two groups of hikers in the Raganello Gorge, which filled with up to 2.5 meters (approximately 8.2 feet) of water, mud and rocks that pushed some bodies as far as 8 kilometers (approximately 5 miles) downstream, BBC News reported.

"A real avalanche of water came unexpectedly. We did not have time to do anything. I was lucky, it was an incredible thing," a Dutch hiker told local media, according to The Guardian.

In total, 23 people were rescued, including four children who had lost one or both of their parents, The Associated Press reported. Some Dutch hikers were among the survivors, but Italian media reports said all the dead were Italian.

"Italy is tired of crying for the dead. Enough," environment minister Sergio Costa said, according to The Associated Press. "If what happened is the result of negligence, sloppiness or a lack of awareness of the risks, we are facing a serious situation that we need to get to the bottom of."

Italian prosecutors opened a criminal investigation into the deaths. The government has also asked for a separate administrative proceeding to see if any negligence caused the deaths.

Investigations will focus on whether weather warnings were issued correctly and whether access to the gorge should have been limited or cut off.

While meteorologists said heavy rains were common in the region during this time of year, rescue workers and park officials said flooding like this hadn't been seen in decades.

"Without a doubt, the event was of a weight we have not seen for many years. We are talking about at least ninety years ago," Pollino National Park President Domenico Pappaterra told Sky TG24, according to The Associated Press.

Pasquale Gagliardi, medical director of the regional helicopter service that airlifted survivors to local hospitals, agreed that it was "unprecedented."

"I've been flying for over 20 years and I can say I'm a veteran. I've helped hundreds of people in difficult situations, but I had never had a misfortune of this size," he told a local newspaper, as BBC News reported.

Costa said rescue workers were "99.9 percent sure" that everyone was accounted for, but that the search was continuing because there is no record of who entered the gorge.

Pappaterra said the national park's guide does not direct hikers through the upper part of the gorge and that only experienced hikers should attempt it, according to The Associated Press.

Some victims were found without proper gear and clothing, according to local media stories reported by BBC News.