Railway officials in India say at least 50 people were killed and more than 100 others were injured when an express train left the tracks on a river bridge. The death toll is likely to rise. More than 300 people have been rescued so far. An investigation has been ordered to ascertain the cause of the accident.

There were nearly 600 passengers and staff on board the train. It was going from the eastern city of Calcutta to New Delhi when it wrecked late Monday night.

The train derailed as it was crossing a bridge over the Dhavi River, near Rafiganj station, in the eastern Bihar State. One of the coaches sank in the river. At least two others hung precariously from the bridge. Several others left the tracks.

The accident occurred in a remote area, with poor telecommunication links. Many victims remained trapped in the wreckage through the night, before they were rescued.

A spokesman for Eastern Railways, Shoumitro Majumdar, said rescue operations are now fully underway, although they were "hampered [a] little bit because of the inclement whether," he said. "There have been heavy rains at times and drizzling most of the times throughout the night. The rescue team, they are trying their best to get the people out as quickly as possible."

Soldiers have joined the rescue operation. The injured people have been taken to hospitals in surrounding towns.

Anxious relatives of passengers crowded the rail stations of Calcutta and New Delhi, waiting for news from the ill-fated train.

The Rajdhani is a luxury train which connects the Indian capital to important cities across the country.

Authorities are offering conflicting statements about the cause of the accident. Junior Minister for Railways Bandaru Dattatreya told reporters he suspects sabotage, because some iron plates that join the tracks had been removed. The accident occurred in an area close to a Maoist guerrilla stronghold. But one hour later, Deputy Prime Minster Lal Krishna Advani said information suggested it was probably an accident.

There are more than 300 accidents every year on India's huge rail network. There are 11,000 trains every day, carrying as many as 13 million passengers. Most of the accidents are minor. But several big accidents in recent years have been blamed on lack of modernization and overcrowding.