Residents of Soi Suksawad 45 and Marine Department officials said the blast was heard on the Smooth Sea oil tanker at 9.20am. The tanker was docked at the IRPC pier.
The explosion produced a billow of black smoke above the oil tanker.
Firefighters from the IRPC and local administration rushed to the scene to fight the blaze and managed to bring it under control at 10.30am.
Four injured workers on the vessel jumped overboard to escape the fire. Three managed to swim to the pier while the fourth went missing, officials said.
A search is on for the missing worker.
The officials have yet to announce the cause of the blast or the extent of the injuries suffered by the workers.
The oil carried by the 3,043-tonne Smooth Sea has a flash point of lower than 60 degrees Celsius.
Firefighters continued to douse the tanker with water to prevent more fires.