At least 11 people were killed in a flash flood in southern Italy when a creek in a mountain gorge swelled suddenly after heavy rainfall, The Guardian reported on Tuesday. The hikers were trekking a gorge located in the Pollino National Park in Calabria region.

Local authorities estimate that five people are still missing, while 23 had been rescued, of which five are in hospital. They said the incident involved two groups of around 18 to 20 hikers each.

“The gorge filled up with water in a really short space of time and these people were catapulted out like bullets,” said Carlo Tansi, head of the civil protection department in Calabria region. “They ended up some 3 km down the valley,” he said, according to Reuters.

“It is a really difficult terrain, filled with obstacles because of the [geological] formation of the area,” said Chief Prosecutor Eugenio Facciolla. Facciolla told BBC that rescuers were trying to locate small patches of land where survivors may have ended up.

An unidentified Dutch hiker said “an avalanche of water came unexpectedly”. “We did not have time to do anything,” the hiker said.

The Raganello creek is a popular trekking spot in the Pollino National Park which is located at the bottom of a narrow, 1-km-deep gorge in the mountain. At its narrowest point, it is just metres wide and some 400 metres tall.