Samsung is rapidly replacing Galaxy Note 7 models that had faulty batteries to limit damage to its reputation, but has been forced to extend the refund period in South Korea after pressure from the safety regulator.

The company said 25 per cent of the 400,000 Note 7s sold in South Korea were replaced and about 500,000 models, about half of those sold in the US, had been turned in.

The smartphone maker said more than 100,000 Note 7 units were replaced in the first three days after it began the replacement programme in its home market, Yonhap reported. Samsung said just 4.5 per cent of Note 7 owners, or about 18,000 people, received a full refund. But the Korean Agency for Technology and Standards asked it to extend the refund offer, which was due to expire on Monday, to the end of the month and to improve battery safety by x-raying Note 7 batteries.

In the US it said most customers opted for a replacement rather than ask for a refund or another Samsung handset.

The world’s largest smartphone maker started issuing replacement devices in South Korea and the UK on Monday, while US replacements started on Wednesday.

Samsung said it will resume selling the Galaxy Note 7 in South Korea on 28 September.

The company also issued a software update that limits Note 7 batteries from charging to more than 60 per cent. Some users have complained that the update restricts charging even on models without the faulty battery.

The company issued a recall for the Note 7 smartphone in early September in 10 markets, including the US and South Korea, after confirming battery problems caused some devices to explode or catch fire.

With an estimated 2.5 million Galaxy Note 7 units sold, analysts say the recall could cost Samsung as much as $5 billion in revenue. The smartphone was launched on 19 August.