Heat is thought to have been the cause of the explosion and fire among containers being stored inside Laem Chabang port in Chon Buri province on Tuesday.
The container in question was holding 378 boxes of organic peroxide in an area reserved for dangerous chemicals.
The fire, which was followed by an explosion, sent a pillar of noxious black smoke into the air, which could be seen from far away.
154 staff of MC logistics company and 23 others from a nearby firm were affected by the smoke.
Seven were sent to a nearby hospital suffering chest tightness.
The emergency services took about half an hour to extinguish the fire and evacuate people.
Witnesses said they saw the flames before hearing an explosion, sending them running out of their offices in panic.
People are still advised to avoid the area, as there is remains a strong odour of chemicals.
