At least thirty people are reported to be injured in the accident.
The accident took place near Trsihuliya Ghat in Ambaji, as the bus expected to be carrying 50 passengers turned over.
Police and rescue teams have reached the site and rescue operations have been launched at the spot on a war footing.
Reacting to the incident, Prime Minister Narendra Modi said he was extremely pained by the loss of lives.
“Devastating news from Banaskantha. I'm extremely pained by the loss of lives due to an accident. In this hour of grief, my thoughts are with the bereaved families. The local administration is providing all possible help to the injured. May they recover soon,” he tweeted.
(This is a breaking news story, further details are waited)