Eighteen people were killed when a truck rammed into a double-decker bus on the Lucknow-Ayodhya National Highway under the Ram Sanehighat police circle.
Fifteen persons have been seriously injured and have been referred to the Trauma Centre in Lucknow.
According to reports, the accident took place in the early hours of Wednesday.
The bus was going from Haryana to Bihar.
According to reports, the double-decker bus on the Kalyani River bridge on the Ayodhya border, was halted following an axle breakdown.
Due to heavy rains and poor visibility, a truck coming from Lucknow at a high speed hit the bus. The collision was so strong that most of them died on the spot.
Most of the bus passengers had got down from the bus and were sleeping on the roadside when the accident took place.
ADG Zone, Lucknow, S N Sabat confirmed the death toll.
After the accident, the national highway was jammed for five kilometres and officials rushed to the spot to rescue the victims and also clear the highway.
Among the deceased, Suresh Yadav, Indal Mahto, Sikandar Mukhiya, Monu Sahni, Jagdish Sahni, Jai Bahadur Sahni, Baijnath Ram and Balram have been identified so far.