At least 18 people have been killed in flash floods near the Dead Sea in Jordan, most of them in a bus that was swept away.
The bus was carrying 37 pupils and seven members of staff to the Zara Maeen hot springs area when it was washed away, officials said.
A huge rescue operation has been launched and Israel said it had sent helicopters at Jordan's request.
So far 34 people have been rescued from the area, Reuters reported.
Some of them are said to be in a serious condition.
The dead and injured also included members of families picnicking at the popular tourist spot.
The Dead Sea is the lowest point on Earth and popular with visitors. But its arid conditions and its deep canyons make it susceptible to flash floods.
Police chief Brig Gen Farid al-Sharaa told state TV that the flash flood had surged for up to 5km (three miles).
"There were people who ended up in the sea water and there were people who managed to reach rocks and save themselves. Thank God we managed to save 13 people without any injuries," he said.
Jordan's King Abdullah cancelled a visit to Bahrain scheduled for Friday because of the tragedy, local media reported.
The Israeli military said that following a request from the Jordanian government, it had sent a number of helicopters with soldiers from an elite search-and-rescue unit.
Troops were helping to locate those missing despite adverse weather conditions, a statement said.
Details of the victims have not been released although an education ministry official said the students were from a private school, the Jordan Times reported.
The official, who was not named, expressed surprise that a school trip had been organised despite weather warnings.
Heavy rain has been sweeping the region for several days. Some streets in the Jordanian capital, Amman, have been inundated, leading to traffic jams, while large hailstorms have been reported elsewhere.
Thursday's incident is the second tragedy resulting from flash flooding near the Dead Sea this year.
In April, nine teenage hikers were swept away and killed in Nahal Tzafit, southern Israel. Another 15 were rescued.