Pakistan Saturday expressed condolences to hundreds of Indian families who lost their loved ones in a horrific three-train collision in Odisha state, the country's deadliest rail accident in more than 20 years.

The state has declared Saturday a day of state mourning as a mark of respect to the victims as 288 people have lost their lives, with more fatalities expected. Over 900 people injured are reported injured in the accident.

Wreckage debris was piled high at the crash site near Balasore, in the eastern state, where some carriages had been tossed far from the tracks and others flipped over entirely.

Smashed train compartments were torn open in the impact late on Friday, leaving blood-stained holes in their sides.

In a statement, Prime Minister Shehbaz Sharif said that he was "deeply saddened" by the loss of hundreds of lives in the Indian train accident.

"I extend my heartfelt condolences to the bereaved families who lost their loved ones in this tragedy. Prayers for speedy recovery of the injured," the prime minister said.

Foreign Minister Bilawal Bhutto-Zardari said he was saddened after learning about the terrible incident.

"Our condolences for the families of the victims. Wish speedy recovery to the injured. #BalasoreTrainAccident," he added.

 The disaster began when an express train running north from India's tech hub Bengaluru to Kolkata derailed, falling onto the adjacent southbound track.

Minutes later, the Coromandel Express heading from Kolkata to Chennai smashed into the wreckage, some of its coaches also colliding with a goods train parked nearby.

India has one of the world's largest rail networks and has seen several disasters over the years, the worst of them in 1981 when a train derailed while crossing a bridge in Bihar and plunged into the river below, killing between 800 and 1,000 people.

Friday's crash ranks as its third worst, and the deadliest since 1995, when two express trains collided in Firozabad, near Agra, killing more than 300 people.

The disaster comes despite new investments and upgrades in technology that have significantly improved railway safety in recent years.

Indian Prime Minister Narendra Modi — who officials said would visit the crash site and hospitals later Saturday — said he was "distressed by the train accident".

"In this hour of grief, my thoughts are with the bereaved families. May the injured recover soon," he tweeted.