More than 60 people have been killed and 100 hurt after a train ran into a crowd near Amritsar in India's northern Punjab state, police told the BBC.
The victims were standing on the railway tracks watching celebrations for Dusshera, a Hindu festival marking the triumph of good over evil.
They did not hear the train approach as they watched a firecracker-filled effigy of the demon king Ravana burn.
Children are said to be amongst the dead.
Spectators were watching the effigy burn, and a fireworks display, when many started moving towards the railway tracks a short distance away.
Some reports suggest organisers told people to move away from the firecrackers, while other reports say participants ran towards the track because they were afraid the burning effigy would collapse.
According to eyewitnesses, many on the tracks were busy filming the festivities on their phones, and did not notice the train approaching at high speed.
Police say the noise of the firecrackers and the crowd may have stopped victims from hearing the train.
The train that hit the crowds was travelling from Jalandhar to Amritsar.
Eyewitness Amar Nath told BBC Punjabi that people were "mauled" by the train.
"I removed the bodies from the tracks... my hands were full of blood."
Local resident Amit Kumar told the BBC the celebrations were a regular occurrence: "Every year, people sit on the tracks when festivities take place here".
Punjab Chief Minister Amarinder Singh described the incident as "absolutely tragic", and wrote in a tweet that local authorities were being "mobilised".
"We will do everything possible to assist the injured," he said, adding: "[I] have directed the district administration to leave no stone unturned to ensure the best possible treatment for them."
He said that victims would be given medical aid for free.
A state of mourning has been declared - offices and schools in Punjab will be closed on Saturday, Reuters reports.
What is the Dusshera festival about?
Celebrates the triumph of the Hindu god Rama over the 10-headed demon king Ravana
Marks the victory of good over evil
In large parts of India it is celebrated with Ramlila - a dramatic folk re-enactment of the 10-day battle
Staged annually - often over 10 or more successive nights
Festival culminates with devotees burning effigies of Ravana which are lit with firecrackers in open grounds
The burning takes place around sunset as Ravana is said to have died when there was "neither sunlight nor dark"
In 2005, Unesco recognised the tradition of Ramlila as a "Masterpiece of the Oral and Intangible Heritage of Humanity"