A passenger train carrying up to 600 people has derailed in Pakistan, sending several carriages plummeting into a ravine.

It is not yet known how many people have been hurt in the incident. Salimur Rahman Akhund, general manager of operations for Pakistan Railways, told the Associated Press news agency that four of the train's carriages had gone into the ravine.

However, other reports said as many as six had plunged over the edge of a 50ft cliff. Army troops have been dispatched to help in the rescue. The accident took place near the town of Jhelum in eastern Punjab province.

The train had been heading to Lahore, the capital of Punjab, from Rawalpindi, a city near Islamabad, when it came off the tracks. Pakistan suffered its worst train crash in a decade last year, when a train driver misinterpreted a signal, pulled into a station and slammed into another train. More than 130 people died in that accident, near Ghotki, in southern Sindh province.