Rescue teams pulled bodies and survivors Monday from the wreckage of two Indian passenger trains that derailed in separate incidents over the weekend, leaving 63 dead and 200 injured.

Nearly a dozen carriages of a packed express jumped the rails in the northern state of Uttar Pradesh on Sunday, while a second derailed as a result of a suspected bomb attack in the restive northeastern state of Assam.

In the first accident, the force of the derailment caused some carriages to mount each other and badly crushed several others, making it difficult for the emergency services to get to survivors.

"We are still searching," the army officer leading the rescue operation, Colonel A.D.S. Dhillon, told AFP by telephone Monday.

"So far we have retrieved 63 bodies from the coaches and we think more people are trapped inside," Dhillon said from the site of the accident, 150 kilometres (95 miles) south of the state capital, Lucknow.

Later Sunday, at least 100 passengers were injured -- 20 of them critically -- when their train derailed in the northeastern state of Assam as the result of what police believe may have been a bomb placed on the rails by separatist rebels.

The Guwahati-Puri Express was nearing Ghograpara, about 70 kilometres from Assam's main city of Guwahati, when it was apparently hit by a strong blast.

"There was a loud explosion and it was total chaos soon after," passenger Jiten Das told AFP by telephone.

"The coach in which I was travelling skidded off the track and fell in marshy land with waist-deep water. Somehow we managed to get out. I cut my head and arms and have a wound in my chest."

Several armed separatist groups are active in the region, but police said the precise cause of the explosion was not yet known.

In Uttar Pradesh, police said at least one Swedish citizen was among the dead from the earlier derailment of the Kalka Mail, which was heading from Howrah, the main station for the eastern city of Kolkata, across India to the capital New Delhi.

The Press Trust of India news agency reported the driver was among the injured and that the train, carrying about 1,000 people, was moving at near its top speed of 108 kilometres an hour when it left the tracks.