Quake-hit Nepal announced Thursday that its long-delayed reconstruction programme would cost 25 percent more than earlier estimated, as millions continue to live in temporary shelters a year after the disaster.

Nearly 9,000 people lost their lives when a 7.8-magnitude earthquake ripped through the Himalayan nation in April 2015, destroying more than half a million homes and prompting the government to peg recovery costs at $6.7 billion.

But Nepal's National Reconstruction Authority (NRA) on Thursday said its five-year recovery plan would now cost $8.4 billion after an ongoing survey of damaged buildings revealed more destruction than earlier estimated.

"The increase was because (early estimates said)... that the completely damaged households would be around 500,000, but that has increased now," said NRA chief Sushil Gyewali.

Gyewali told reporters it would also cost more to build quake-resistant schools than previous estimates had suggested.

In the weeks following the disaster, the world rallied to help the desperately poor country rebuild, promising $4.1 billion in aid.

But delays in setting up the NRA and formulating a reconstruction plan has seen Nepal's government sign deals to receive just $2.3 billion so far, around half the amount pledged.

Stung by criticism, the government has vowed to kickstart the reconstruction of schools and hospitals and speed up the distribution of the first $500 instalment of a $2,000 payout promised to millions of homeless victims.

An estimated four million people are still living in sub-standard temporary shelters, according to the International Federation of Red Cross and Red Crescent Societies.