At least 13 people have died and about 50 are injured after two passenger trains collided in India's southern Andhra Pradesh state on Sunday.

A rescue operation was launched and hundreds of emergency workers were at the site to clear the wreckage.

Officials said a preliminary investigation has found that a "human error" had led to the collision.

Prime Minister Narendra Modi expressed his condolences and said he was in touch with the railways minister.

The crash took place in the Vizianagaram district on Sunday evening.

Officials said three carriages of a passenger train, travelling between Visakhapatnam and Palasa, derailed around 19:00 (13:30 GMT) after it was hit by another train.

The train had stopped on the tracks "due to a break in an overhead cable" when a second incoming passenger train travelling between Visakhapatnam and Rayagada rammed into it from behind, a railway official told Reuters news agency.

Hundreds of ambulances, doctors, nurses and rescue personnel were sent to the scene to rescue passengers and pull out bodies.

Biswajit Sahu, Chief Public Relations Officer of East Coast Railway, said that a "human error" had led to the collision, caused by "overshooting of signal" by the second train.

He added that 33 trains had been cancelled and 22 others had been diverted following the accident. Railway officials expect the affected track to be cleared for traffic to resume by Monday evening.

Andhra Pradesh's Chief Minister YS Jagan Mohan Reddy's office said he would visit the site of the accident on Monday. The minister has also announced financial compensation for the victims.

India has one of the largest train networks in the world with millions of passengers using it daily, but a lot of the railway infrastructure needs improving.

Sunday's accident comes just months after a devastating crash involving three trains killed 292 people and injured thousands more in the eastern state of Odisha.

The country's top detective agency arrested three railway employees in connection with the railway accident, which was the worst in 20 years. Source BBC