A speeding train packed with passengers travelling to join their families for Eid festival derailed in Pakistan's southern Sindh province on Wednesday, killing nearly 50 people and injuring 150 others.

Fourteen of the 16 coaches of the Karachi Express jumped the tracks at Mehrabpur in Naushero Feroze district at 2.25 am (2.55 am IST) while it was on its way from this port city to Lahore [Images], the capital of Punjab province.

Nearly 50 people lost their lives in the accident, officials said.

Caretaker Railways Minister Mansoor Tariq confirmed at least 45 deaths while Pakistan Army said it had evacuated 38 bodies and 150 injured people from the site.

President Pervez Musharraf [Images] ordered an immediate inquiry by the Pakistan Railways into the causes of the accident and directed authorities to fix responsibility.

Railways general manager Asad Saeed, meanwhile, said a broken track joint caused the derailment and ruled out the possibility that the accident occurred due to a terrorist activity.

"A welded track joint broke. Tracks shrink in winter. There are many forces on the track and sometimes a joint breaks," he said.

The railway tracks are old and government is replacing them. An investigation has been ordered to ascertain the exact cause of the accident, Saeed said.

Some of the derailed coaches were badly mangled when they slammed into each other as they hurtled off the tracks. People remained trapped in the damaged coaches for up to 10 hours after the accident and officials said the death toll could rise.