Israeli rescue services personnel operate near the site where a group of Israeli youths was swept away by a flash flood, near the Zafit river bed, April 26, 2018. Photo: Reuters / Amir Cohen.

At least nine teenage seminary students died after they were swept away by a flash flood in the Negev Desert in southern Israel on Thursday, an ambulance service said.

Military helicopters and search and rescue units scoured the Zafit river bed that flows into the rift valley at the southern end of the Dead Sea after a flash flood caught a party of 25 trekkers in the usually bone-dry area by surprise.

Another student was unaccounted for and the search was suspended as night fell and heavy thunderstorms returned to the region, police said.

Prime Minister Benjamin Netanyahu described the event as a “terrible disaster” and praised rescuers for their efforts.

After two days of heavy rainfall, normally arid river beds that run from west to east have filled up and deposited surges of water into the Dead Sea and the rift valley region that runs south along the Negev Desert.