A passenger bus fell into a deep ravine near El Karma in Algeria, killing 27 people and injuring 39, Health Minister Mohamed Seddik Ait Messaoudene said.
The bus had set out from Setif for the capital, Algiers, and crashed about 50 kilometres before reaching its destination.
It left the road after the driver lost control, before falling into the ravine.
Rescue teams began operations after receiving the alert at 9:40 a.m. local time, Algeria's Civil Protection said.
Civil Protection said the cause of the crash had not yet been determined and was under investigation.
Ait Messaoudene warned that the casualty toll could rise.
Prime Minister Sifi Ghrieb visited injured people being treated at Boumerdes University Hospital.
President Abdelmadjid Tebboune declared three days of national mourning.
Tebboune said those found responsible would face strict legal action once the investigation is completed.
Algerian road-safety authorities have identified speeding and other human errors as leading contributors to road crashes in the country.