DARKUSH, Syria (AP) — At least seven people drowned and 20 were injured, most of them children, when a school bus skidded off the road and plunged into a river in northwestern Syria on Thursday, emergency responders said.

The accident happened near the town of Darkush, west of the city of Idlib, where the bus plunged into the Orontes River, a local civil defense organization also known as the White Helmets said in a statement.

Rescue teams searched for about six hours for survivors in the cliffside and in the river, it said.

It was not immediately clear what caused the bus to go off the road. Images from the scene showed a steep crag overlooking the riverbed where searchers were scrambling over boulders.

Ahmad Ghandour, a doctor at the hospital in Darkush that received the casualties, said the students and teachers on the bus were from a school for orphans.

It was the latest tragedy to affect an area that has already been hit hard by Syria’s ongoing civil war and by a devastating 7.8 magnitude earthquake that hit Turkey and northern Syria last year.

Most of most of the 5.1 million people living in opposition-held northwestern Syria have been internally displaced, sometimes more than once, in the country’s civil war, now in its 14th year, and rely on aid to survive.