A labor rights group marked yesterday's launch of Apple's latest iPhone with a report accusing one of the smartphone giant's Chinese suppliers of exploiting factory workers.

Hong Kong-based Students and Scholars Against Corporate Misbehavior say Lens Technology, which makes touchscreen glass, used forced overtime, withheld wages and risked workers' health after a months-long investigation into three of its factories.

Company founder Zhou Qunfei, herself a former factory worker, became China's richest woman after Lens Technology's debut on the Shenzhen stock exchange in March.

As the iPhone 6S went on sale in markets including China and Japan, SACOM called for Apple to "apply immediate measures to rectify exploitations in its supply chain." In a statement it said: "We urge Apple Inc to fulfill its corporate responsibility ... to give workers a workplace with dignity and respect."

The rights group's allegations include workers going for a month without a day off, wages being withheld for weeks and the company failing to pay social security.

"Dust, noise, polluted water and chemical substances are common problems on the shop floor," it added, with management "ignoring if workers were well-protected."

It sent undercover workers into factories, as well as interviewing workers off-site.

Around 10 protesters gathered outside one of Apple's largest stores in Hong Kong yesterday morning, holding giant phones with the slogan "Throw Away The Bad Apple."

But the hundreds of customers who had pre-ordered one of the new phones were largely oblivious.

"I think bad conditions happen to all brands," said James Leung, 30, who was waiting to pick up a rose-gold phone for his wife, which he said cost him HK$5,000 (US$645).

"For me, I need a phone, so I'll get a new phone."

Lens Technology, which also supplies Samsung and other leading tech firms, primarily makes touch-sensitive glass covers for mobile phones, computers and cameras.

SACOM spokeswoman Liang Pui-kwan said the group was not only targeting Apple.

"But Apple is the richest and has the biggest ability to make change and bring the industry forward," she said.

"We're trying to bring the facts in front of people and let them know what they are choosing."

Lens Technology and Apple were not immediately available for comment.

Earlier this year a SACOM investigation prompted Japanese clothing giant Uniqlo to promise to improve working conditions at its Chinese suppliers after claims employees were being put at risk.

The report accused Uniqlo of buying from two suppliers in south China's Guangdong Province that made employees work long hours for low pay in unsafe conditions.

The iPhone 6S features a new "3D Touch" feature that allows users to differentiate between a light touch and a harder tap, with the phone reacting differently to each.

In Asia-Pacific, the phone was launched in Australia, China, Japan, New Zealand and Singapore yesterday.