India struggles as millions throng banks to swap high denomination notes
Indelible ink will be used to mark the fingers of people swapping scrapped currency notes at banks as authorities in India struggle to deal with the bedlam caused by the sudden demonetising of the country's highest-denomination bills.
India announced a week ago that it was withdrawing 500 and 1,000 rupee notes as legal tender to fight corruption and tax evasion.
However, people are allowed a one-time swap of 4,000 rupees (£47) at any bank in exchange for smaller notes to meet immediate needs.
Overwhelmed banks have been unable to ensure that people do not line up more than once, since identification such as drivers' licences and passports are not linked to bank or tax accounts.
Economic affairs secretary Shaktikanta Das said there have been reports of "unscrupulous people" who have organised groups of innocent people and sent them from bank to bank to swap old notes.
India also uses indelible ink to mark the fingers of voters after they cast their ballots in elections.
Larger amounts of demonetised notes can be deposited in saving accounts before the end of the year. However, people depositing big amounts are likely to find tax officials looking into their finances.
There are also limits to the amount that can be withdrawn from accounts and ATMs.
Hundreds of millions of Indians do not have bank accounts and use only cash. Many small businesses accept only cash.
Banks have been swamped throughout the week as people have thronged to exchange currency notes or withdraw their weekly limit of 2,500 (£30) from ATMs.
The government says it is trying to rush the printing of new 500 and 2,000 rupee bank notes, but has not been able to keep up with demand.
Banks and ATMs run out of cash well before the end of work hours, leaving millions of people stranded without money.
The government says the demonetising of big currency notes is expected to bring billions of pounds into the economy and tax base, long hobbled by corruption and money laundering.
Businesses routinely use cash to avoid paying taxes. Raids on corrupt politicians and businesses regularly uncover large stashes of money.