The incident took place at Bhagwanpur in Roorkie. People from nearby villages rescued those trapped inside the mangled bus.
The bus was on its way from Saharanpur in Uttar Pradesh to Haridwar in Uttarakhand.
The bus driver, Raj Kumar, suddenly had a fit and could not control the vehicle. To avoid a major mishap, he rammed it into a roadside tree on the Delhi-Dehradun highway.
The injured passengers were mostly from Haryana, Jammu and Uttar Pradesh.
Get the latest election news, live updates and election schedule for Lok Sabha Elections 2019 on ndtv.com/elections. Like us on Facebook or follow us on Twitter and Instagram for updates from each of the 543 parliamentary seats for the 2019 Indian general elections.