Three of the world's largest IT companies said yesterday that they were investigating working conditions at Foxconn after a series of suicides at the huge manufacturing plant in southern China they use to make electronic goods.

Nine workers at Foxconn's Shenzhen plant, which employs and houses 300,000 people, have died after falling off buildings since the beginning of this year, the latest on Tuesday. Police have confirmed seven of the cases as suicide. Two other workers attempted to kill themselves by jumping off buildings but survived.

The suicides have forced the normally secretive Taiwanese company – which makes products such as smartphones and digital cameras under contract for many of the world's biggest technology companies – to be more open about its working practices.