The explosion at the Tupras oil refinery in the Izmir region was an "industrial accident, there was no external interference or attack", said Bayram Yilmaz, the senior local official in the area, quoted by the state-run Anadolu news agency.
Investigators were at the scene to find out what technical issue had caused the blast at the plant of Tupras, Turkey's only oil refiner which is owned by the giant Koc industrial holding company.
Blast-ripped industrial zone a hub for Chinese, foreign firms
Reports said the accident was caused by a build-up of gas during maintenance.
Turkish officials acknowledge the country has shortcomings in industrial safety but legislation had been tightened since 301 miners were killed in May 2014 following a fire at the Soma coal mine in western Turkey.
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