Kolkata: Polling began under heightened security in 49 constituencies spread over two districts - Howrah and North 24 Parganas - bordering Kolkata in phase four of the West Bengal assembly polls here on Monday.

North 24 Parganas, a part of which falls under the world's largest mangrove forests - the Sundarbans - has 33 constituencies. The remaining 16 are in Howrah.