The crash occurred at about 1:45 a.m. on 2 August, 1999, when the Avadh Assam Express from New Delhi collided with the Brahmaputra mail at Gaisal railway station, Uttar Dinajpur, West Bengal, 19 kilometers from Kishanganj.

Through a signaling error at Kishanganj, the Avadh Assam Express from Delhi was transferred onto the same track as the mail train.

The staff at intermediate stations between Kishanganj and Gaisal also failed to notice that the Assam express was on the wrong track.

As a result, Brahmaputra Mail train crashed headlong into the front of the Avadh Assam Express at Gaisal.

[1] The Avadh Assam Express WDM-2 locomotive was thrown high in the air, and passengers from both trains were propelled into the neighbouring buildings and fields by the force of the explosion.

[citation needed] The line was blocked by wreckage, and the Gaisal emergency services were utterly overwhelmed, as fire swept through the ruined vehicles and station buildings, killing many of the injured people trapped in the trains.

Many vehicles and aid support services had to undertake the 14-hour drive from Calcutta to reach the site, by which time many of those they could have helped were already dead.

Heavy rains helped dampen fires the following day, and rescue workers began trying to separate the twelve mangled carriages of the train and identify the bodies contained inside.

Because of the nature of the crash and fire, as well as the large number of ticketless people who may have been on the trains, the bodies could not be separately identified.