Factories manufacturing Apple iPads and iPhones in China are forcing staff to sign pledges not to commit suicide, the Daily Mail reported citing a probe.

After a spate of suicides last year, managers at the factories ordered new staff to sign pledges that they would not attempt to kill themselves, according to researchers, the report quoted sources as saying. 

At least 14 workers at Foxconn factories in China have killed themselves in the last 16 months as a result of horrendous working conditions. Many more have attempted suicides or been stopped before trying at the Apple supplier's plants in Chengdu or Shenzen, according to the report.

An investigation of the 500,000 workers by the Centre for Research on Multinational Companies and Students and Scholars Against Corporate Misbehaviour (Sacom) found appalling conditions in the factories.

Demand for Apple iPhone and iPad products is so high that workers in China who assemble them are treated inhumanely, like machines to keep up output, it said.

Leontien Aarnoudse, a Sacom official said the workers were asked to work overtime to meet increasing demands for the products. They work excessive overtime for a salary they can hardly live on and are inhumanely treated, said Aarnoudse.

Conditions are harsh and they don't have a social life. Their life is just working in a factory and that's it, Aarnoudse added.