By Subir Bhaumik BBC correspondent in Calcutta

Police in the Indian state of West Bengal say at least 50 people are missing after a mechanised boat capsized in a river in the state's Sundarbans region.

The mechanised boat carrying around 100 passengers capsized mid-stream in the Matmatla River at midday (local time).

Police say local fishermen in the Sundarbans rescued between 50 and 60 people, but no fewer than 40 were still missing, feared drowned.

Police say they have fished out five dead bodies from the river so far.

Rescue operations are continuing.

Strong currents

The mechanised boat was travelling from Sonakhali to Kultoli, two remote localities in the Sundarbans delta region, south of Calcutta, when it capsized.

Police officials said more bodies were likely to be recovered, but some might be washed downstream to the sea by strong currents in the Matmatla River, which flows into the Bay of Bengal.

Such accidents are not rare in the Sundarbans delta, where roads are rare and ports are often the only means of transport.

They are poorly maintained and more often than not overcrowded.

Neighbouring Bangladesh, where ferries are also a common means of transport, suffers from regular ferry disasters, sometimes involving large loss of life.