Over 50 complaints of such withdrawals were received in two days in two city police station areas. The crime was reported from other Bengal districts as well, said a senior police officer, here on Tuesday.

"57 complaints were received between Sunday and Monday. 44 cases of fraudulent withdrawals were received by the Jadavpur police station. The Charu market police station recorded 13 such complaints on Monday," said the officer as long queues of panicky customers were seen at bank kiosks, frantically updating their passbooks.

According to Joint Commissioner (Crime) Murlidhar Sharma, the fraudulent withdrawals were being done from Delhi. The anti-bank fraud section was investigating the matter, he added.

"Our team has reached Delhi. We have received some CCTV footage and are looking into them," said Sharma. Two cases had been registered in Jadavpur and Charu Market police stations by clubbing all the complaints, he added.

Last year, fraudsters had withdrawn large amounts by attaching skimming devices to some ATMS in south Kolkata areas, like Gariahat, Lake Gardens and Jadavpur. The police had then arrested a gang of Romanians for the crime. The gang members are still in jail.

Preliminary enquiries into the latest cases too point to involvement of such gangs that installed skimming devices to clone debit cards, Sharma said.

According to sources, some CCTV footage from Delhi ATMs have pointed to some suspects seen withdrawing money wearing caps and masks. Police suspect a three-member gang was involved in the crime in Delhi.

With a number of affected customers having accounts in the Punjab National Bank, an official on Tuesday assured them they would be refunded the missing money within 15 days.

"I would like to assure all our customers on behalf of the bank that they need not worry. Whatever losses they have suffered will be compensated by the bank. The process for returning the money to their accounts has started. The money will be credited within 15 working days," the official said.

Many tense and apprehensive bank customers queued up at bank kiosks through the day.

"A person living on the upper floor flat of my apartment lost money due to fraud. So I came here to update my passbook to check if everything was fine," said a senior citizen.

Standing in the queue at the teller counter of a bank branch, a young woman said she had stopped using ATMS or doing online transactions.

"I am not going to ATMs. I don't have the confidence after what all have happened. I have come to my branch all the way to withdraw money. I don't have the guts to do any more online transactions", she said.

Meanwhile, a teacher at Kirnahar of the Birbhum district said Rs 80,000 had been withdrawn from his bank account. The teacher had apparently withdrawn Rs 6,000 from an ATM in Bolpur. Three days later, Rs 80,000 was withdrawn from his account through two transactions of Rs 40,000 each.

He lodged a police complaint and informed his bank, and got to know that the money was withdrawn from two ATMs in Delhi and Jadavpur.

A similar complaint was registered in East Burdwan district also.

As a preventive measure, the city police have decided that motor cycle patrol teams from every police station would check ATMs, especially those without any security guard, twice a day to prevent attachment of any skimming device. He advised ATM users to change their PIN at least once every six months.

"We have also spoken to bank officials to get the money of the affected depositors back," Sharma said.

He said some banks, including the SBI, had introduced a feature in their apps by which customers could activate their ATMs just before use and deactivate them after that. "If you take such steps, you won't have to face harassment," he said.