Police said the accident took place this afternoon when a Sonauli-bound state roadways bus collided with a private bus near the approach road of Maniram Bridge, about 20 kms from the city.
While 15 passengers were killed on the spot, five others succumbed to injuries at BRD Medical College Hospital.
Commissioner Ravindra Naik announced an ex-gratia of Rs 50,000 for the kin of each of the deceased and Rs 25000 to the seriously injured. Rs 10,000 each will be given to persons with minor injuries.
Senior officials inspected the accident site and visited the hospital where at least half a dozen people are stated to be critical.