Four persons died on the spot and two others succumbed to injuries while receiving treatment following the accident which took place along a highway last night, police said.
The bus en route to Nepalgunj from Narayanghat lost control and overturned in Ghodaha forest of Devdaha along the East-West Highway in Rupandehi district.
Of the 16 injured, condition of four is critical. They have been sent to Bharatpur for further treatment.
Poor road infrastructure and reckless driving are the leading causes of accidents in Nepal.
As per the Nepal's traffic police data, on an average five to seven people are killed in road accidents every day in the country.