The plan to withdraw high-value rupee notes in India had to be kept secret, Prime Minister Narendra Modi has said.
Four days after the launch of the anti-corruption move, long queues continue outside ATMs as people try to exchange the 500 ($7) and 1,000 notes.
“It had to be done suddenly but I never thought I will receive blessings for this,” Mr Modi said.
He hinted that other measures aimed at fighting corruption and the black economy might follow.
Urging people to be patient, Finance Minister Arun Jaitley said that it would take a few weeks for banks and ATMs to completely replace the old notes, estimated to make up some 85% of the total currency in circulation.
Mr Jaitley said that nearly $30bn in the old notes had so far been deposited in banks across the country.
But chaotic scenes can still be witnessed outside banks as public patience is beginning to wear out, says the BBC’s Sanjoy Majumder in Delhi.
Some traders and small business owners have threatened to go on strike because they have been badly affected, our correspondent says.
The opposition has also been critical of the move, saying the rural and urban poor have been hit hardest.
But Mr Modi thanked his fellow countrymen who had “accepted the decision in national interest”.
And he warned that there was “no guarantee” that new measures would not follow after the note-exchange scheme ends on 30 December.
He said “no-one would be spared” in the drive against corruption. But “honest people will not face any problem”, he added.
After Mr Modi’s surprise announcement on Tuesday night, the banks were closed on Wednesday.
Thousands of panicked Indians have been flocking to banks since they reopened on Thursday.
There are limits on cash withdrawals from ATMs and banks.