Carriages were reduced to twisted metal
The accident happened at dawn near the town of Ghotki in Sindh province. The trains were packed with passengers.
Police said a train travelling to Karachi crashed into a broken-down train, catapulting carriages across the track into the path of another train.
The general manager of Pakistan Railways said the crash was caused by a train conductor misreading a signal.
People are crying, fathers are looking for children, husbands for their wives and brothers for their sisters
Witness
In pictures: Train crash Crash site horror
Medical officials collating casualty figures from hospitals in the area said the death toll was expected to rise. A number of the injured are in a critical condition.
At least 13 train carriages were derailed. Shocked survivors described being thrown from their beds and seats.
"I woke up at the noise of a huge bang and then there was [a] big jerk and smoke all over the place," injured passenger Mohammad Amin told Reuters news agency.
"There was total darkness... I hit the floor and fainted."
Rescue workers have been cutting through twisted metal to reach the dead and injured trapped inside the wreckage. Bodies were strewn across the tracks.
The army has cordoned off the crash site, and troops are helping with the rescue effort.
The crowded trains collided in a devastating chain of events
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Train traffic along Pakistan's main north-south route has been badly disrupted, and a special relief train to bring survivors back to Karachi has been cancelled.
Worried families in Karachi have headed to the city's main train station, but officials said they had no passenger lists.
Many families are renting private cars in an effort to reach the crash site and look for loved ones, many of whom where thought to be holidaymakers from Karachi.
"It is a very gruesome situation," said police official Aga Mohammed Tahir.
One witness told AFP news agency: "It's a painful scene. There are bodies scattered all over.
HAVE YOUR SAY There are many in my carriage who have been badly injured or even died
Mohammed Akhtar, Karachi, Pakistan
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"People are crying, fathers are looking for children, husbands for their wives and brothers for their sisters."
The accident happened at about 0400 (2300 GMT Tuesday) on the border between the provinces of Sindh and Punjab.
The express train heading from Lahore to Karachi slammed into the rear of broken down Quetta Express at a station near Ghotki, about 600km (370 miles) north-east of Karachi.
A third train travelling in the opposite direction, heading from Karachi to Rawalpindi - the Tezgam Express - then hit a number of derailed carriages, which were scattered over several tracks.
Abdul Wahab Awan, general manager of Pakistan Railways, said the conductor of the Karachi Express had failed to read a signal correctly.
The Karachi train was travelling at 120km/h (75mph) when it struck the stationary train, a senior railway official told AFP.
The injured have been taken to hospitals in three nearby towns. A doctor at a hospital in Sukkur said about a dozen people there were in a critical condition. Some of the injured had lost limbs or suffered terrible head injuries.
Pakistani President Pervez Musharraf said he was "deeply saddened" at the crash and ordered an urgent investigation.
Pakistan is no stranger to train crashes involving multiple deaths. The BBC's Paul Anderson says casualty figures are often so high because trains are packed with far greater numbers than they were designed for.
More than 200 people were killed in a train crash in Sindh province in 1990. The following year more than 100 people were killed in another accident, also in Ghotki.
PAKISTAN TRAIN CRASH 1. Quetta Express, travelling from Lahore to Quetta, is stationary for maintenance work 2. Karachi Express, travelling from Lahore to Karachi, crashes into Quetta Express. Carriages derail across other tracks. 3. Tezgam Express, travelling from Karachi to Rawalpindi, crashes into derailed carriages
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Your comments:
Horrific is the only word that can describe this. I survived by pulling myself from metal and glass around. Horrific experience, my thoughts and prayers are with the family and friends of the victims.
Jameel Rehman, Lahore, Pakistan
It is such a horrible sight. I myself have fortunately survived, but there many on my carriage who have been badly injured or even died. I can only pray for the families of those who have died.
Mohammed Akhtar, Karachi, Pakistan
In Pakistan, this is not a new thing. We still run our trains on age old tracks. Our signal system is very out of date.
Mukhtar Azad, Karachi, Pakistan
Today early in the morning the first news I heard was this railroad accident. My uncle was in the Karachi Express with his family. My father called me up and was crying and not even able to talk what happened. The news took the soul out of me, as last Sunday he was here visiting us after several years. Luckily he and his family survived and we were relieved after 3 hours of the worst ever suffering.
Waseem Riaz, Chakwal, Pakistan
It is pathetic to hear about this sad news with the loss of so many lives. It is the responsibility of the Pakistani government to look after their people and provide the best technology available for public transportation.
Mohammed Imam, Raleigh, USA
My prayers are with all those who have suffered in this tragedy. I hope that the Pakistani government will rethink its budget and divert from military spending to building a reliable infrastructure for ordinary Pakistanis.
Nayo, Lancashire, UK
I have travelled on this route several times. I am really shocked and horrified. I will certainly not travel on trains any more. I can well imagine that the government will conduct superficial inquiries and after four weeks this accident will be treated as a bygone matter. Pakistan has to learn a lesson with this tragic accident. Well organized and business oriented railways can generate enough money to invest in technological upgrading.
Imran Ahsan Mirza, Lahore, Pakistan
It's about time that Pakistan Railways invested in new tracking systems, better equipment and more training facilities for current personnel.
Omer, UK
I am deeply saddened that so many people have lost their lives in such a horrific way. All we can do now pray on behalf of the deceased and their families and hope that the Pakistani government decides to invest in the best for the country. These trains are far unsafe for passengers because they are archaic, not managed efficiently, and are not designed to cater for the huge numbers of people that use the service on a daily basis.
Bilal Khan, Kingsbury, London
If it was really a human error, training camps should be set in order to train those drivers not to make such mistakes ever. The issue is sensitive and the devastation caused due to driver's mistake is much more expensive than training them not to make those mistakes! There should not be any economical concerns for going to such trainings and for giving moral support to those drivers.
Fahad J Khokhar, Lahore, Pakistan
Very sad to know of so many casualties in today's rail accident. The government needs to take strict action against people responsible for this carelessness to avoid future loss of valuable lives. It also needs to improve and modernize its transport system.
Aziz, Rawalpindi
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Liczba ofiar porannego zderzenia trzech pociągów w miejscowości Ghotki w pakistańskiej prowincji Sindh wynosi od 112 do 150. Lokalne media informują, że liczba ofiar może nawet wzrosnąć do trzystu. 

Przedstawiciele pakistańskich linii kolejowych powiedzieli reporterom Associated Press, że wypadek wydarzył się około 4 nad ranem czasu lokalnego (1 w nocy czasu polskiego), kiedy pocąg ekspresowy  z Lahore do Karachi zderzył się z innym składem, stojącym na stacji. Trzeci pociąg uderzył w nie w wyniku wykolejenia się części wagonów. 

Maszynistę pociągu do Karaczi obwinia się za spowodowanie wypadku.

Jest to największy wypadek kolejowy w Pakistanie od grudnia 1989 roku, kiedy w wypadku niedaloko Sangi (około 55 km od miejsca dzisiejszej katastrofy) zginęło ponad 400 osób.