A bus veered off a mountain highway and crashed into a river in western Nepal on Tuesday, killing at least 27 people and injuring another 11, police said.

Police official Lal Bahadur Pandey said the accident took place before dawn near Parkha village, about 400 kilometers (250 miles) northwest of the capital Katmandu.

The area is a remote mountainous region where the roads are narrow and have hairpin turns.

The cause of the crash — in which the bus rolled about 300 meters (1,000 feet) before it landed in a river — was not immediately known.

Not many vehicles travel along the highways in the area, and Pandey said the accident wasn't noticed until a passing vehicle spotted it after sunrise. Rescuers have been sent to the area.

Bus accidents in Nepal are mostly blamed on both poorly maintained vehicles and roads.