Samsung unveiled two upgraded folding smartphones on Wednesday as the South Korean sector leader sought to head off rising competition from Chinese firms in a fast-evolving market.

The Galaxy Z Fold3 and Z Flip3 offer sleeker designs, improved water resistance and more durable screens are available for pre-ordering for delivery later this month in the United States, Europe and South Korea.

The new devices come with Samsung facing heightened competition from Chinese manufacturers including Xiaomi, which grabbed the number two position in the second quarter.

The Flip3, with a 17 centimetres display, will start at $999, in line with other premium and flagship devices, and the 19 centimetres Fold3 at $1,799.

"Samsung is once again redefining the possibilities with foldable smartphones that empower users with the flexibility and versatility needed for today's fast-paced world," said TM Roh, head of Samsung mobile.

"These devices equip consumers with technologies that unlock new ways to maximise and enjoy every moment with an ecosystem built on openness and innovation."

The Flip3 aims to offer an affordable foldable, and the Fold3 aims to replace the large-screen devices and will include a retractable pen than can be used on the screen.

A recent survey by the research firm Canalys showed Chinese electronics firm Xiaomi has overtaken Apple as the number two global smartphone maker in a market in turmoil due to a global chip shortage and consumers emerging from lockdowns.

The Canalys survey showed worldwide smartphone sales up 12 per cent, with South Korea's Samsung holding its top position with a 19 per cent market share.

Xiaomi meanwhile surged to the number two position for the first time ever with a 17 per cent share as sales jumped 83 per cent, according to Canalys.

Apple dropped to number three with iPhone sales up just one per cent, after getting a lift from last year's new models.

Chinese makers Oppo and Vivo held fourth and fifth place in the global market, each with around 10 per cent, according to Canalys.

Smartphone sales were up 11 per cent from last year but down from the first quarter as manufacturers struggled with a global shortage of semiconductors, according to the research firm.