Thousands of Chinese factory workers will be given the chance to detail the punishing conditions on assembly lines producing Apple iPads and iPhones, after the US company bowed to criticism and agreed to allow independent inspections of its supply chain.

Facing a growing scandal over the working conditions of those making its best-selling gadgets, Apple has called in assessors from the same organisation that was set up to stamp out sweatshops in the clothing industry more than a decade ago. The move is an admission that Apple's own system of monitoring suppliers has failed to stamp out abuses, and that the negative publicity surrounding its Chinese operations threatens to cause a consumer backlash against its products.

But campaigners for Chinese workers immediately criticised the company for conducting a public relations exercise instead of actually alleviating the long hours, harsh management and safety problems which have driven some workers to suicide and led to fatal accidents at a number of plants.

Inspectors from the Fair Labour Association started work yesterday at the Foxconn factory near the booming southern city of Shenzhen, where iPads are made. In 2010, a spate of 13 suicides or attempted suicides at that factory, known as Foxconn City, first turned a spotlight on the companies Apple uses to build its devices. Another Foxconn factory in Chengdu will also be inspected, Apple said, with the first findings to be published by the FLA next month. Apple said all of its suppliers had agreed to co-operate with the FLA and to let their workers speak freely.

Apple has come under fire for building a consumer electronics powerhouse on the backs of exploited workers, many of whom earn as little as 30p an hour. Employees of some suppliers complain of 10-hour shifts with only one permitted break, and of being forced to stand for so long that their legs swell. Last year, there were two fatal explosions at plants producing Apple goods, including one caused by the ignition of dust released by the polishing of new iPads.

The FLA will ask employees about working and living conditions, including health and safety, pay and hours. Its team will inspect manufacturing areas, dormitories and other facilities.

"We believe workers everywhere have the right to a safe and fair work environment, which is why we have asked the FLA to independently assess the performance of our largest suppliers," said Apple's chief executive, Tim Cook. "The inspections now under way are unprecedented in the electronics industry."

Apple's decision to call in the FLA comes after a new round of exposés of conditions at its suppliers. Last week, the campaign group China Labour Watch wrote an open letter to Mr Cook demanding that Apple accept lower profits so suppliers can raise wages, employ more staff and invest in improving safety.

Yesterday, the organisation dismissed Apple's commitment to independent inspections as a publicity stunt. "We already know what the conditions are like in the factories," said Fan Yuan, a China Labour Watch activist. "What Apple needs to do right now is take action to solve the problems. This move is not really about solving the problems, but rather about Apple getting publicity and rebuilding its positive image."

The FLA was set up in 1998 to monitor a code of practice introduced by clothing manufacturers that aimed to stamp out sweatshop conditions among their suppliers, following a similar public outcry and the success of consumer boycotts of offending companies.

Its work comes in addition to the audits conducted every year by Apple itself, which introduced a code of practice limiting the length of workers' shifts and demanded proper overtime pay. The company's spot-checks, though, reveal scores of violations at most suppliers.

Mr Cook, who took over the leadership of Apple last year from the late Steve Jobs, is fêted as the architect of its lean and flexible supply chain, which has been central to its ability to turn devices from concept to mass production in a matter of months. He has also focused on getting products produced at the lowest possible costs, which is one of the reasons that Apple's profits are among the fattest in the technology industry.

Yesterday, Apple's share price passed $500 for the first time in its history, just seven months after it first topped $400. The company is now the most valuable in the world, at $460bn.

Apple in China: The allegations

In July 2009, a Foxconn employee fell from an apartment building after losing an iPhone prototype. Over the next two years, at least 18 more of the company's workers have attempted suicide or have fallen from buildings in ways that suggested suicide.

In 2010, 137 workers at the Suzhou facility owned by Apple suppliers Wintek were injured after being ordered to use a poisonous chemical, n-hexane, to clean iPhone screens because it dried faster. Although Apple claims to have contacted all the employees affected, many say they have heard nothing.

In May 2011, four employees were killed and 18 were injured in a dust explosion at a Foxconn factory in Chengdu, which produces iPad parts. Chinese campaigners claim they warned Apple of hazardous conditions at the plant.

In December 2011, another 61 workers were injured in a gas explosion at the Riteng Computer Accessory Co factory in Shanghai, which was trialling aluminium iPad 2 back panels.

Employees allege that many of Foxconn's dormitories, where 70,000 workers live, are overcrowded, with reports of 20 workers being housed in a three-room apartment.