At least 18 people, most of them children, have been killed after raging floodwaters swept away a school bus near the Dead Sea.

Jordan launched a major operation on Thursday to search for survivors involving army divers, and neighbouring Israel said it was assisting with search-and-rescue helicopters.

Search teams had rescued 34 people, some of whom were in a serious condition, Jordanian civil defence sources said. The bus had been carrying about 40 children and their teachers.

Many of those killed were children under 14. A number of families picnicking in the popular destination were also among the dead and injured, rescuers said, without giving a breakdown of numbers.

Hospitals in the area were put on high alert. A civil defence official was quoted on state television as saying that the number of casualties was expected to rise.

Israel’s police and military said their forces were sent at the request of the Jordanian government. “The soldiers … are assisting in locating the missing in spite of the adverse weather conditions,” the Israeli Defence Forces said.

The region was bracing on Thursday for the first winter storms after the summer, with heavy rainfall and high winds expected.

In a separate incident a four-year-old was killed in southern Israel when he was swept away by flooding, local media reported.

In April, nine Israeli teenagers hiking south of the Dead Sea were killed in a similar flood. The arid region, the world’s lowest point at about 1,400ft (430m) below sea level, is often hit by flash floods.

They occur when heavy rains hit higher ground, even while the local area is dry, with torrents rushing down steep cliffs and cutting across roads.