BANGKOK (AP) -- Explosions and a fire in one of the world's largest petrochemical plants have killed 12 and injured more than 100 people in eastern Thailand.

The blaze at a factory belonging to Bangkok Synthetics, a synthetic rubber manufacturer, forced an evacuation of workers and more than 1,000 residents Saturday in Rayong province, 180 kilometers (110 miles) southeast of Bangkok.

Rayong governor Seni Jittakasem said Sunday that authorities are investigating the cause of the explosions that started when workers were cleaning a chemical tank.

The fire was brought under control after four hours of chemical burning that sent plumes of thick smoke over a wide area. Seni said all evacuees had returned home by Sunday.