They say the collision happened at Arrakkonam station, near Madras (Chennai).

Some 50 people were injured in the incident, India's TV channels say.

It was not immediately known how many people were on board the two trains. Emergency teams have been sent to the accident site.

The official said that five bodies had already been recovered.

Some people are still believed to be trapped in the carriages, and the authorities warn the death toll may rise further.

Accidents are common on the state-owned Indian railway, an immense network connecting every corner of the vast country.

It operates 9,000 passenger trains and carries some 18 million passengers every day.