Indians have declared almost US$10 billion in hidden wealth under a government amnesty on tax evasion, as part of Prime Minister Narendra Modi's moves to crack down on huge piles of black money.

Finance Minister Arun Jaitley said the four-month scheme that closed on Friday had resulted in 64,275 declarations of previously undisclosed assets and income, totaling 652.5 billion rupees (US$9.8 billion).

"With so many people declaring money it shows a significant number of people want to become tax compliant," Jaitley told reporters in New Delhi on Saturday.

"This figure could be revised upward once the final tabulation is done," the minister said, adding that the additional revenue would help fund public welfare schemes.

India's taxpayers are startlingly few, with only around 2.5 percent of its 1.2 billion population filing returns -- largely because the so-called unorganised sector employs so many people who are paid cash.

Modi vowed to crack down on tax avoidance to tackle the country's yawning inequality after storming to power at elections in 2014.