A fire at a chemical company in the South Korean city of Ulsan forced about 7,000 nearby workers to evacuate on Wednesday, Yonhap and Seoul Economic Daily reported.

The fire started at about 9:41 a.m. at the plant in the Onsan National Industrial Complex, Seoul Economic Daily reported. Ulsan is about 310 kilometers southeast of Seoul, Yonhap reported.

The blaze began at an outdoor tank holding 8,000 liters of toluene, a liquid that burns easily, both outlets reported. Five or six explosions were heard before flames shot up, Seoul Economic Daily reported.

All 16 workers inside the plant escaped on their own, Seoul Economic Daily reported. No injuries were reported.

As black smoke spread, refiner S-Oil stopped part of the work at its nearby Shaheen project site, and about 7,000 workers there moved to safety, both outlets reported.

Wind carried embers that started a second fire on a lawn at a nearby business, Seoul Economic Daily reported. The local government sent a text alert asking drivers to take other routes and telling residents to be careful.

About 200 personnel and three helicopters were sent to fight the fire, Yonhap reported. Interior Minister Yun Ho-jung ordered officials to use all available resources and to check for anyone missing.

The fire was fully put out at 1:50 p.m., about four hours after it started, Yonhap reported in a later update. The fire is believed to have started as toluene was being moved into drums. It then spread to tanks holding other hazardous materials, including acetone and ethanol.

A company official told police and fire officials that he heard a blast and an electrical spark near the piping at the tank's inlet, Seoul Economic Daily reported. He shut off a valve, and then the explosion happened.

Police and fire officials plan to look into the exact cause of the fire, Yonhap reported.

What we know: The fire was put out after about four hours, and no injuries were reported.
What we don't: What exactly caused the fire.