Buses stand in front of the entrance of Wistron, a Taiwanese-run iPhone factory, at Narsapura, Bengaluru. AFP

Thousands of workers ransacked the Narasapura industrial area around 6am. As of Sunday, the police had arrested 128 people in connection with the violence.

Apple Inc said it is investigating if its Taiwanese contractor Wistron Corp flouted supplier guidelines at a violence-hit iPhone manufacturing facility near the Indian city of Bengaluru, following violence at the plant.

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Violence breaks out at India iPhone factory near Bengaluru

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Prashanth TD, administrative office, had said in his complaint that a group of outsiders armed with iron rods and clubs forced its way into the premises and targeted the HR block first.

An Apple logo is seen on the outside of an Apple store in San Francisco, California. File/AFP

Wistron is one of Apple's top global suppliers. In India, it makes iPhone 7 handsets and second-generation iPhone SE devices.

Workers at Apple's Taiwanese contract manufacturer Wistron’s factory in Narasapura, about 70km from Bengaluru, went on rampage on Saturday morning over alleged non-payment of wages and extended working hours.

Unidentified factory workers trashed the facility on the outskirts of Bengaluru over the weekend as employees demanded unpaid wages and better working hours, trade union representatives said.

A private security personnel guards the entrance of a Taiwanese-run iPhone factory at Narsapura, Bangalore. AFP

Apple demands its suppliers provide safe working conditions, treat workers with dignity and respect, act fairly and ethically, and use environmentally responsible practices wherever they make products or perform services for the company.

Wistron said it was "deeply shocked" by the violence, which it blamed on "unknown persons... with unclear intentions".