India's largest state bank is looking to expand it customer base by encouraging sex workers to deposit their nightly takings in a savings account.

The State Bank of India will relax some rules to accommodate potential clients from Sonagachi in central Calcutta, one of Asia's biggest the red light districts, its assistant manager, Ranajoy Ghosh, said.

"Tomorrow we will open accounts for 300 sex workers in Sonagachi, where an estimated 30,000 brothel-based sex workers are operating," he said.

"You can say it's a little recognition for the sex workers who are fighting for legal status for their profession and social recognition," Mr Ghosh said.

The bank has reduced the required minimum deposit from 500 rupees to 300 rupees and will forgo the lengthy verification procedures normally required for new clients, Mr Ghosh said.